GB1591598A

GB1591598A - Method for producing a cement-bondes floor

Info

Publication number: GB1591598A
Application number: GB1986678A
Authority: GB
Original assignee: CEMPRO AG
Current assignee: CEMPRO AG
Priority date: 1977-05-18
Filing date: 1978-05-16
Publication date: 1981-06-24
Also published as: ATA347178A; DE2722624A1; CH633065A5; AT372469B; FR2391336A1; DE2722624C3; FR2391336B1; DE2722624B2

Abstract

In order to be able to work a sufficiently thick layer (3), consisting of granolithic concrete aggregate, into the mortar layer (2), which is not set, of a screed, a concrete plasticiser with a low content of surface-active agent is applied to the stiff-plastic mortar layer (2) and rubbed in with the granolithic concrete aggregate which has likewise been applied. In the case of a granolithic concrete aggregate for use in the process, at least some of the bodies (12) are at least partially provided with an envelope (13) of a concrete plasticiser. <IMAGE>

Description

(54) METHOD FOR PRODUCING A CEMENT-BONDED FLOOR (71) We, CEMPRO A.G., a Joint Stock Company organised under the laws of Liechtenstein of Mitteldorf 1, FL 9490 Vaduz, Liechtenstein do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to a method for producing a cement-bonded floor, in which a hard aggregate is worked into a layer of mortar which has not yet set.

In industrial installations, floors of high strength are used on a large scale and these floors must have a high capacity to withstand rolling and sliding friction. With normal cement floors whose aggregates consist of pit sand or river sand (which comprises quartz), it is possible to achieve high compressive strength and tensile bending strength with a correspondingly high ratio of cement, but not the resistance to abrasion required by high quality industrial floors. Therefore, in order to produce high quality cement-bonded industrial floors, special additives, so-called hard material mixtures or hard aggregates are used. In comparison to aggregates normally used, hard aggregates of this type are very expensive.For example, at the present time, river sand costs approximately 30 DM/tonne, whereas, depending on the hardness, hard aggregates cost approximately 130 to 1 80DM/tonne or even approximately 1800 to 2,500DM/tonne (electrocorundum and silicon carbide).

Since, on account of the inevitable irregularities of the concrete foundation, industrial floors generally cannot be produced below thicknesses of 25 to 30mm, for which purpose, according to the ratio of the mixture, approximately 30 to 45kg hard aggregate per square metre are required, it is not possible for reasons of cost to produce cementbonded industrial floors for relatively high stresses completely using such hard aggregates.

Essentially, two methods are known for managing with less hard aggregate per square metre of floor surface: In one method, the floor is produced from normal aggregates with a cement content (and water-cement ratio) which produces the desired strength, and the required resistance to abrasion is achieved due to the fact that the hard aggregate which was previously mixed dry with the cement, is spread on the floor which has not yet set and then rubbed into the surface structure.

During this rubbing-in operation, compacting of the new floor takes place. This has the result that excess cement and, in an even greater quantity, excess water, come to the surface, resulting in the dry material which has been spread out being absorbed into the mortar mixture. This causes the following drawbacks: If the floor is produced with a stiff plastic consistency, then its absorption capacity for the hard aggregate applied subsequently is limited. At best, 2 to 3kg of a hard aggregate mixture can be worked into the surface structure of such a stiff plastic mortar per square metre. This relatively small quantity is only able to form a very thin layer for resisting wear, the average depth of the layer being less than lmm.

However, if the consistency of the floor is made softer, so that as a result of a greater excess quantity of mixing water and cement flue, larger quantities of a hard aggregate spread on the surface of the floor can be absorbed, for example 8 to 10kg/m2, would lead to a wear-resistant surface layer having a depth of approximately 5 to 6mm, then the hard aggregate can be rubbed into the mortar structure more easily. However there is the drawback that the hard aggregate sinks into the mortar owing to its relatively high specific gravity so that after the layer of mortar sets, the hard aggregate is no longer on the surface, but is located below a relatively soft and insufficiently resistant layer of cement of insufficiently resistant fine mortar.

In another known method, the floor is laid in two layers. To equalize the levels and to provide an adequately flat foundation, a floor is firstly laid using normal plain aggregate (river sand, fine gravel etc.), which generally has a minimum depth of 20mm, because with thinner floors, problems as regards the mortar and operating problems would occur. Immediately thereafter, the socallcd wear-resistant layer is applied to the first layer, i.e. one new layer on top of another, which wear-resistant layer contains the above-mentioned hard aggregate and also contains cement as the bonding agent.

Because layers of mortar can only be laid with great care in thicknesses of less than lOmm, the thickness of the wear-resistant layer is generally lOmm. Only when using very expensive hard aggregates (electrocorundum, silicon carbide) are wear-resistant layers used with a thickness of 8, sometimes even of 6mm, which requires a high degree of skill and great care.

When producing two-layer floors of this type, considerable technical problems arise, which have not bcen overcome hitherto. In order to achieve an adequate bond between the levelling layer and the wear-resistant layer, it is absolutely necessary that the two layers are laid fresh-on-fresh, i.e. that the levelling layer has not yet set when the wearresistant layer is applied. In order to achieve the highest possible strength, the wear-resis tant layer should be produced with a relatively low water-cement ratio, i.e. should have the stiffest possible plastic consistency.

However, this is impossible since in order to eliminate cavities which lead to a reduction in the strength, stiff plastic floor mortar must be compacted by tamping or vibrating, which is not possible with a floor whose levelling layer located therebelow has not yet set and would therefore be deformed at the time of this tamping or vibrating.

Therefore, when producing two-layer floors of this type, it is indispensable to mix the mortar of the wear-resistant layer with a very soft plastic consistency, i.e. with a relatively high content of mixing water, so that it can be easily compacted.

However, due to the high water-cement ratio, the strength which can be achieved in the wear-resistant layer with respect to the value which can be achieved theoretically drops and also as a result of the difference in the gross density between the cement glue and the hard aggregate, the soft mortar tends to separate when laid so that the lighter cement glue and the lighter aggregate rise to the surface and the heavier hard aggregates sink to the bottom. This again produces a surface with lower abrasive resistance than should be able to be achieved theoretically by the use of hard aggregates.

The invention intends to develop the aforementioned first method so that whilst eliminating the drawbacks described, a wearresistant layer of high quality and with a depth of several mm can be produced.

According to the present invention there is provided a method of producing a cementbonded floor in which an aggregate having a hardness greater than that of quartz is worked into a layer of mortar which has not set, wherein the mortar is produced with a stiff plastic consistency, and the aggregate is worked into the layer of mortar with a concrete plasticise having low surface activity (as herein defined).

Preferably the aggregate is worked into the mortar by rubbing.

The advantage of the invention consists in that due to the fact that the concrete plasticiser is introduced into the mortar at the same time as the hard aggregate and that the concrete plasticiser penetrates the layer of mortar no deeper than the grains of the hard aggregate, at least not substantially deeper, the hard aggregate is prevented from sinking too deep into the mortar layer, so that the hard aggregate remains in the region of the surface, whose resistance to wear is intended to be increased. Since the concrete plasticiser penetrates the layer of mortar at the same time as the hard aggregate, working-in the grains of hard aggregate into the mortar layer causes no difficulties, but can take place very quickly and easily. Due to this, a layer of appreciable thickness, for example up to 6 mm, can be strengthened with the hard aggregate.By means of the working-in operation, insofar that it has been given a very soft plastic consistency by the concrete plasticiser, the mortar is also compacted, if the layer of mortar was not previously adequately compacted. This also increases the strength of the wear-resistant layer.

It was found that when using concrete plasticizers which are surface-active agents, i.e. appreciably reduce the surface tension of the water, considerable evaporation of the mixing water takes place, so that adequate hydration is prevented and the wear-resistant layer has only inadequate strength. Therefore it is proposed according to the invention to use a concrete plasticizer which has a low surface activity. This means that the concrete plasticizer either does not reduce the surface tension of the water at all, or only by a negligible amount. In a concrete plasticizer which contains a mixture of substances, this should mean that surface active agents contained in the mixture of substances either alone or as a result of the presence of further substances, have no harmful effect on the surface tension of the mixing water.

The concrete plasticizer can be applied to the layer of mortar before or after the application, for example by spreading, of the hard aggregate, depending on the state of aggregation of the concrete plasticizer. The plasticizer can be spread, atomized or sprayed on. One embodiment of the invention is particularly advantageous in which the hard aggregate and concrete plasticizer are spread together on the layer of mortar.

The afore-described method has a further advantage: if the layer of mortar is given a very stiff plastic consistency, in order that after working-in, the hard aggregate which is spread thereon is located directly in the region of the surface of the layer of mortar, then this layer of mortar can only be compacted in an unsatisfactory manner. Despite treatment by tamping or vibrating, mortar layers of this type generally have a porosity of between 10 and 15%. However, for its strength, any porosity of concrete or cement mortar is tantamount to an excess amount of mixing water for the same volume.However, since the strength of concrete or mortar (depending on the standard strength of the cement used) is determined solely by the ratio of the water and cement in the fresh mortar, this means that: floor mortars for hard aggregate floors are generally made with a cement content of 400kg/m3 and a water-cement ratio of 0.4 (i.e. an overall water content of 160kg/m3).

They thus reach strengths of approximately 5000 to 5,500N/cm2. Now if, in the compacted state, this floor mortar still has 12% porosity, i.e. 120 litres per m3, then this is the same as if its overall water content had been increased from 160 litres to 280 litres and its water-cement ratio from 0.4 to 0.7.

However, an increase in the water-cement ratio of 0.4 to 0.7 means a reduction in strength of at least 50% (c.f. Walz: relationships between the water-cement ratio and compressive strength of concrete).

As a result of this relatively low strength of the mortar layer below the wear-resistant layer, the load-carrying capacity of the wearresistant layer is limited as a result of the low load-carrying capacity of its foundation.

According to a further development of the invention, in which a cement mortar with a water-cement ratio corresponding to a stiff plastic consistency is used in manner known per se to produce the mortar layer, this drawback is eliminated by the use of a further concrete plasticizing agent which is added to the mortar before producing the mortar layer, the effectiveness of which agent ends before the beginning of setting of the concrete and that after the end of the effectiveness of the further concrete plasticizing agent, the hard aggregate and the concrete plasticizer having a low surface activity are applied to the layer of mortar and the hard aggregate is worked-in.

In this respect, the advantage consists in that due to the use of the further concrete plasticizing agent, the layer of mortar has a very soft plastic consistency despite a very low water-cement ratio, so that it can be well compacted without difficulties and therefore has a high degree of strength after setting and hardening. However. this soft plastic condition does not last until the beginning of setting, but ends much sooner, so that the layer of mortar then has a stiff plastic consistency and when the hard aggregate and concrete plasticizer are spread-out and worked-in, the grains of the hard aggregate cannot sink undesirably into the mortar layer.

This embodiment of the method according to the invention provides a completely compacted monolithic floor layer, in whose upper region the grains of the hard aggregate are embedded and protect the surface of the floor effectively against abrasion. Also, there is no danger of damage to the floor when considerable intermittent stress occurs.

The effectiveness of the further concrete plasticizing agent may last approximately 30 minutes for example, whereas the time from producing the mortar to the beginning of setting amounts to 3 to 4 hours for example.

Also, taking into consideration the time necessary for producing the layer of mortar, there is adequate time for spreading and working-in the hard aggregate and concrete plasticiser between the period when the further concrete plasticising agent looses its plasticising effect until the concrete begins to set.

The concrete plasticiser and the further concrete plasticising agent may be different substances. However, substances with the same effective components are preferably used, the further concrete plasticising agent is preferably identical to the concrete plasticiser. If a material is used as the further concrete plasticiser, whose plasticising effect ends after a relatively short time, then this has the advantage that after rubbing the hard aggregate into the surface of the mortar layer, only a relatively short period of time passes before it is possible to walk on the floor, so that any subsequent work on the floor is possible very quickly, for example, it is also possible to spread even more hard aggregate with concrete plasticiser on a point of the floor which has already been treated and likewise to work this into the latter.

The invention also relates to an aggregate which is particularly suitable for carrying out the method according to the invention. According to this aspect of the invention, we provide an aggregate material comprising a granular aggretate (e.g. with a granular size of approximately I mm.) which has a hardness greater than that of quartz, the granules of said aggregate being at least partially coated with a concrete plasticiser having low surface activity (as hereinbefore defined).

This provides the advantage that the hard aggregate can be used very simply and that no special attention needs to be paid to measuring the quantity of concrete plasticiser to be applied to the surface of the layer of mortar.

Further features and advantages of the invention will become apparent from the following description of embodiments of the invention with reference to the drawings: Figure I is a cross section through a floor before and after rubbing-in the hard aggregate.

Figure 2 is a simplified, greatly enlarged cross section through one grain of hard aggregate, which has a complete coating of a concretc plasticizer and Figure 3 shows one grain of the hard aggregate. which is only partly coated with concrete plasticizer.

A layer 2 of cement mortar having a thickness of approximately 25mm is applied in figure I to an uneven concrete foundation 1, which may be the rough floor of a factory for example. One cubic metre of cement mortar contains 400kg cement and 160kg water as well as sand and aggregate. This mortar mixture has a stiff plastic consistency.

When producing this mortar mass, a concrete plasticizer was also added at the rate which gives the mortar mass a soft plastic consistency despite the low water-cement ratio.

The layer 2 was then produced with this soft plastic mortar. The concrete plasticizer looses its effect approximately 30 minutes after mixing with the remaining mortar and after this period of time, on account of its low water-cement ratio, the mortar mass has a very stiff plastic consistency and can be walked on.

Hard aggregate, for example silicon carbide, with a fine grain, possibly with a grain size of below 1 mum, together with the same concrete plasticizer which was used for producing the mortar layer 2 is now spread on the surface and rubbed into the mortar layer 2 in known manner. In this way, a layer 3 is formed in the upper region of the mortar layer 2, which layer is strengthened considerably with hard aggregate and gives the surface of the mortar layer 2 high resistance to abrasion. In figure 1, the layer 3 is only shown in the right-hand part.

Cement is added to the hard aggregate when the latter is spread out (one part by weight cement to two parts hard aggregate), so that the water-cement ratio of the uppermost region of the layer 2 decreases further and the strength is thus increased.

The finished floor has a very high compressive strength and resistance to impact on account of the high strength of the cement layer 2, furthermore it has a very high resistance to wear on account of the hard aggregate used.

Figure 2 is a greatly enlarged view of one grain 10 of the hard aggregate and the latter is shown diagrammatically in cross section, which grain has a complete coating 11 of the concrete plasticizer.

Figure 3 shows a similar grain 12, comprising only a partial coating 13 of concrete plasticizer.

The quantity of concrete plasticizer applied to the grains 10 and 12 in the form of the coating I 1 or 13 is measured such that when the grains spread on the surface of the mortar layer 2 are rubbed-in, in the immediate vicinity of the grains, the mortar which has not yet set is made plastic to an adequate extend so that the grains can be rubbed-into the mortar layer 2 without difficulty, but do not sink too deep into the mortar layer 2.

The coating can be produced using a solution, in particular an aqueous solution of the concrete plasticizer, or the material forming the coating sticks by simple adhesion, which can be improved by previously moistening the grains.

The same concrete plasticizer is preferably used both when producing the mortar layer 2 and when rubbing the aggregate grains into the mortar layer. Also, the coating 11, 13 preferably consists of the same concrete plasticizer which is used for producing the mortar layer 2.

The concrete plasticizer is a so-called chemical plasticizer. The following substances are suitable for this: Water soluble melamine resins which are produced under the (Registered Trade Mark) "Melment" by the Siiddeutsche Kalkstickstoff-Werken of Trostberg; Water soluble phenolic resin condensates produced by Rtag AG of Essen; Water soluble formaldehyde resins produced by the company Rohm & Haas, Philadelphia, U.S.A. under the Registered Trade Mark "Orotan".

In the embodiment described, the mortar of the layer 2 is plasticized twice with the concrete plasticizer, the first time when producing the layer 2, the second time when rubbing-in the hard aggregate.

WHAT WE CLAIM IS: 1. A method of producing a cementbonded floor in which an aggregate having a hardness greater than that of quartz is worked into a layer of mortar which has not set, wherein the mortar is produced with a stiff plastic consistency, and the aggregate is worked into the layer of mortar with a concrete plasticiser having low surface activity (as herein defined).

2. A method as claimed in claim 1 wherein the aggregate and the plasticiser are applied together on the layer of mortar.

3. A method as claimed in claim 2 wherein the aggregate and the plasticiser are applied to the mortar layer by spreading.

4. A method as claimed in any one of claims 1 to 3 wherein, to produce the layer of mortar, a cement mortar with a cementmortar ratio providing a stiff plastic consistency is used, a further concrete plasticising

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. Further features and advantages of the invention will become apparent from the following description of embodiments of the invention with reference to the drawings: Figure I is a cross section through a floor before and after rubbing-in the hard aggregate. Figure 2 is a simplified, greatly enlarged cross section through one grain of hard aggregate, which has a complete coating of a concretc plasticizer and Figure 3 shows one grain of the hard aggregate. which is only partly coated with concrete plasticizer. A layer 2 of cement mortar having a thickness of approximately 25mm is applied in figure I to an uneven concrete foundation 1, which may be the rough floor of a factory for example. One cubic metre of cement mortar contains 400kg cement and 160kg water as well as sand and aggregate. This mortar mixture has a stiff plastic consistency. When producing this mortar mass, a concrete plasticizer was also added at the rate which gives the mortar mass a soft plastic consistency despite the low water-cement ratio. The layer 2 was then produced with this soft plastic mortar. The concrete plasticizer looses its effect approximately 30 minutes after mixing with the remaining mortar and after this period of time, on account of its low water-cement ratio, the mortar mass has a very stiff plastic consistency and can be walked on. Hard aggregate, for example silicon carbide, with a fine grain, possibly with a grain size of below 1 mum, together with the same concrete plasticizer which was used for producing the mortar layer 2 is now spread on the surface and rubbed into the mortar layer 2 in known manner. In this way, a layer 3 is formed in the upper region of the mortar layer 2, which layer is strengthened considerably with hard aggregate and gives the surface of the mortar layer 2 high resistance to abrasion. In figure 1, the layer 3 is only shown in the right-hand part. Cement is added to the hard aggregate when the latter is spread out (one part by weight cement to two parts hard aggregate), so that the water-cement ratio of the uppermost region of the layer 2 decreases further and the strength is thus increased. The finished floor has a very high compressive strength and resistance to impact on account of the high strength of the cement layer 2, furthermore it has a very high resistance to wear on account of the hard aggregate used. Figure 2 is a greatly enlarged view of one grain 10 of the hard aggregate and the latter is shown diagrammatically in cross section, which grain has a complete coating 11 of the concrete plasticizer. Figure 3 shows a similar grain 12, comprising only a partial coating 13 of concrete plasticizer. The quantity of concrete plasticizer applied to the grains 10 and 12 in the form of the coating I 1 or 13 is measured such that when the grains spread on the surface of the mortar layer 2 are rubbed-in, in the immediate vicinity of the grains, the mortar which has not yet set is made plastic to an adequate extend so that the grains can be rubbed-into the mortar layer 2 without difficulty, but do not sink too deep into the mortar layer 2. The coating can be produced using a solution, in particular an aqueous solution of the concrete plasticizer, or the material forming the coating sticks by simple adhesion, which can be improved by previously moistening the grains. The same concrete plasticizer is preferably used both when producing the mortar layer 2 and when rubbing the aggregate grains into the mortar layer. Also, the coating 11, 13 preferably consists of the same concrete plasticizer which is used for producing the mortar layer 2. The concrete plasticizer is a so-called chemical plasticizer. The following substances are suitable for this: Water soluble melamine resins which are produced under the (Registered Trade Mark) "Melment" by the Siiddeutsche Kalkstickstoff-Werken of Trostberg; Water soluble phenolic resin condensates produced by Rütag AG of Essen; Water soluble formaldehyde resins produced by the company Rohm & Haas, Philadelphia, U.S.A. under the Registered Trade Mark "Orotan". In the embodiment described, the mortar of the layer 2 is plasticized twice with the concrete plasticizer, the first time when producing the layer 2, the second time when rubbing-in the hard aggregate. WHAT WE CLAIM IS:

1. A method of producing a cementbonded floor in which an aggregate having a hardness greater than that of quartz is worked into a layer of mortar which has not set, wherein the mortar is produced with a stiff plastic consistency, and the aggregate is worked into the layer of mortar with a concrete plasticiser having low surface activity (as herein defined).

agent is added to the mortar before spreading thereof to form the mortar layer, said further plasticising agent being one which ceases to be effective before the mortar begins to set, the aggregate and the concrete plasticiser having low surface activity are applied to the layer of mortar and worked into said layer when said further plasticising agent has ceased to be effective.

5. A method as claimed in claim 4 wherein said concrete plasticiser having low surface activity and said further concrete plasticising agent contain the same active ingredients.

6. A method as claimed in any one of claims 1 to 5, wherein the aggregate is worked into the layer of mortar by rubbing.

7. A method as claimed in any one of claims 1 to 6 wherein the aggregate is silicon carbide.

8. An aggregate material for use in the method of any one of the preceding claims, comprising an aggregate having a hardness greater than that of quartz, the grains of said aggregate being at least partially coated with a concrete plasticiser having low surface activity (as herein defined).

9. A method of producing a cement bonded floor substantially as hereinbefore described with reference to any one of the accompanying drawings.

10. A cement bonded floor when produced by the method of any one of claims 1 to 7 or claim 9.

11. An aggregate material as claimed in claim 8 substantially as hereinbefore described with reference to Fig. 2 or Fig. 3 of the accompanying drawings.