GB2135665A - Polymer cement mortar composition - Google Patents

Abstract

A polymer cement mortar composition suitable for use as a coating applied to steel structures, metal roofs, external walls, civil engineering structures, etc. comprises an aggregate (e.g. granulated blast furnace slag) (S) having a glass content of 95% or over, a styrene-butadiene polymer (P) and a cement (C), the weight ratios C/S and P/C being from 0.4 to 0.65, and from 0.2 to 0.5.

Description

SPECIFICATION Polymer Cement Mortar Composition The present invention relates to a polymer cement mortar composition which is used by applying to steel structures, metal roofs, external walls, civil engineering structures, etc.

Anti-corrosion paint is typical of coating materials used for steel structures. While the anticorrosion painting consists of simply applying or spraying a suitable anti-corrosion paint to the surface of a steel structure and it can be effected very easily, there have been disadvantages that the anticorrosive property for a steel structure subjected to a coating treatment employing a anti-corrosive paint is low in durability, particularly low in abrasion durability since the coating film thickness is generally small and that it is difficult to expect that the coating continues to exhibit the desired effect under natural and artificial environments over a long period of time.

Under these circumstances, the method of applying cement mortar and forming an anti-corrosive layer on steel structures has been studied and carried out in some quarters with a view to ensuring the desired durability. However, the most serious disadvantage of the cement mortar application is that the applied coating layer tends to cause cracks therein.

Thus, in view of the cracking tendency of applied coating layers after hardening, attempts have also been made to use cement compositions premixed with asphalt, for example, and these attempts have been disadvantageous in that not only the surrounding environment such as the soil is contaminated by the various constituents exuded from the plasticizer used but also the offensive smell emitted by the asphalt affects seriously the operators as well as the inhabitants in the neighborhood.

In view of these circumstances, so-called polymer cement mortar compositions incorporating synthetic resin components in place of asphalt have come into use.

These polymer cement mortar compositions have been used as paving materials, waterproof materials, chemical resistant coatings, ship's deck coverings, vehicles lining materials since the incorporated polymers have been considered to have the effect of increasing the cohesion of the hardened cement and improving the adhesion to steel structures and to be useful from the characteristic and anti-corrosion effect of view of the compositions as construction materials.

The required characteristic properties for these applications have included the adhesion to ground or priming, abrasion resistance, waterproofing effect, weathering resistance, cracking prevention, impact resistance, chemical resistance, expansion and contraction property, anti-corrosive property for structures to be coated, etc., and the polymer cement mortar compositions now in use have been considered to satisfy the most of these requirements.

However, these known compositions have still left room for improvement so as to fully and satisfactorily meet the characteristic properties required by ever divergently increasing various applications. Some examples of these deficiencies will be described in detail hereunder.

(1) The known polymer cement mortars mostly employ latex or emulsion polymers of the water dispersion type which are mixed with hydraulic cement, aggregate, etc., and they exhibit a rapid rusting phenomenon upon expiration of a few minutes after the coating. Such a rapid rusting phenomenon is called as a flush rust and the results of experiments have shown that this phenomenon takes place in substantially all the polymer cement mortars to different extents.

When such a flush rust occurs, particularly when the steel structure is placed in a corrosive environment after its occurrence, this, coupled with an expansion in the volume of the rust on the steel surface, tends to cause danger of peeling off.

This is due to the fact that no consideration has been given to the anti-corrosive properties of the polymer emulsions incorporated in the known polymer cements, While it is generally considered that the alkali of the cement makes the steel to passive state, for this purpose it is necessary to maintain the pH of the cement coating 12 or over at the steel surface and thus it is dangerous to overestimate the anti-corrosive effect of the polymer cement simply due to its alkaline nature. In other words, Fig. 1 shows the relation between the pH and the corrosion of the steel according to the research works of W. Whiteman and R. Russel and it will be seen that the corrosion of the steel progresses rapidly when the pH is less than 1 Also, the following Table and Fig.

2 show the results obtained by stirring and mixing 100 grams of the aggregate, cement, etc., of the samples 1 to 7 shown in the Table with 900 cc of tap water, hanging down a polished mild steel sheet into each of the resulting still liquids, measuring the variations in the pH value of the liquids with a pH meter and observing the occurrence of rust.

Sample No. Aggregate, Cement etc. Condition After 30 Days Immersion 1 Tap water (blank) Uniform rust X 2 Portland cement No rust (i) 3 Portland blast furnace cement No rust 0 4 Slag Uniform rust X 5 Cement 30+slag 70 Rust around specimen holes 0 6 Cement 30+silica sand 70 ,, 0 7 Sand Uniform rust X

It has been found that while the pH values were low and considerable rust occurred in the case of the tap water (blank), the slag and the sand, the portland cement and the portland blast furnace cement showed high pH values (12 or over) on the average and no occurrence of rust and the cement plus slag and the cement plus silica sand showed slightly lower pH values and the occurrence of slight rust on the specimens.

(2) Although the known polymer cements mortars are anti-corrosive materials, no satisfactory consideration has been given to the surface preparation and the coating system with the result that when the cements are placed in corrosive environments (e.g., exposed places or places subjected to the alternate wet and dry conditions in the seaside area), rust is caused between the steel surface and the coating material in a very short period of time and this causes deterioration of the adhesion.

In accordance with the results of various extensive studies made from the above-mentioned points of view, an anti-corrosive coating composition comprising a cement, a granulated blast furnace slag of a specified particle size and a polymer emulsion mixed together in specified quantities or proportions has been proposed (Japanese Patent Publication No. 5739661) and also a polymer cement mortar has been developed (Japanese Patent Publication No. 58-38378) which comprises a mixture of a hydraulic cement and a water dispersion type polymer as a constituent of the composition and separately incorporates an anti-corrosion agents.However, various other properties, such as, elongation, thermal shock resistance and abrasion resistance are also required and cases frequently occur where the conventional polymer cement mortar compositions are not only incapable of fully meeting these severe requirements but also incapable of coping with the requirements depending on the applications.

As the result of earnest and constant research works conducted for the purposes of developing a polymer cement mortar composition having improved properties so as to satisfy the requirements of such ever increasing applications as mentioned previously, the inventors have discovered and invented a novel polymer cement mortar composition which comprises a polymer, a cement and an aggregate as principal essential components and in which the aggregate consists of specially selected one thereby satisfactorily meeting the previously-mentioned various required properties.

It is therefore an object of the present invention to provide a polymer cement mortar composition comprising a cement (C), an aggregate (S) and a polymer (P), which is characterized in that the aggregate consists of one having a glass content of 95% by weight or over and the polymer consists of d styrene-butadiene polymer and that the C/S ratio and the P/C ratio are respectively selected from 0.4 to 0.65 and from 0.2 to 0.5 by weight ratio.

Fig. 1 is a graph showing the behavior of the corrosion rate of steel in pH atmosphere.

Fig. 2 is a graph showing the changes of pH value with day when mild steels were immersed into waters having different kinds of aggregates dispersed therein.

Fig. 3 is a graph showing in terms of maximum strain (Smax) the resistance to bending (f) and the resistance to compression (C) of end products due to variations in the glass content of the aggregates incorporated in polymer cement mortar compositions.

Fig. 4 is a graph showing the effect on the strength of polymer cement mortar composition by the mixing ratio of the cement (C) and the slag (S) in polymer cement mortar compositions.

Fig. 5 is a graph showing the effect on the peeling strength of polymer cement mortar composition by the mixing ratio of the polymer (P) and the cement (C) in polymer cement mortar compositions.

Fig. 6 is a graph showing the peeling strength of end product to various materials.

Fig. 7 is a perspective view showing the relation between a peeling strength measuring jig and a test specimen.

Fig. 8 is a perspective view for explaining a test specimen after an abrasion test.

Fig. 9 is a graph showing the behavior of change with time of the abrasion tests.

Fig. 10 is a graph showing the damping behavior of steel plates coated with polymer cement mortars.

Fig. 11 is a graph showing the stress-strain behavior of test specimens prepared by using polymer cement mortar compositions.

Fig. 1 2 is a graph showing the dimensional changes with time of the test specimens prepared by using polymer cement mortar compositions and subjected to cyclic thermal test.

The cement component used by this invention comprises a portland cement, portland blast furnace cement or the like and the principal functions expected of this component are the improvement of strength and durability and the maintenance thereof.

Also, the polymer used comprises a styrene-butadiene type polymer such as styrene-butadiene polymer or acrylic modified styrene-butadiene polymer. When a polymer of any other type than this type is used, it is difficult to obtain the desired effects with respect to the adhesion between the compositibn and an object to be coated and/or the flush rust preventive effect as shown by the results of preliminary studies which will be described later.

In accordance with the invention, it is also an essential requirement to use an aggregate having a glass content of 95% by weight or over.

In the case of the ordinary polymer cement mortar compositions, they are made by using aggregates comprising silica sand such as river sand or pit sand, granulated blast furnace slag or the like.

However, when the polymer cement mortar compositions using these aggregates are used in civil engineering applications, that is, when they are applied as paving materials or external wall materials, they have the disadvantage of tending to cause cracks.

In completing the invention, preliminary studies have been made on the various polymers (P), the various aggregates (S), the P/C and C/S weight ratios with respect to the cement (C) and other general tendencies and the below-mentioned results have been obtained.

Shown in the following Table are the results obtained by applying to steel plates polymer cement mortar compositions each made by adding to a cement component comprising a portland blast furnace cement one of the following polymers as the polymer component and one of the following anticorrosive agents in an amount corresponding to 0.5% by weight of the whole composition to examine the effect of the anti-corrosive agent addition and observing the subsequent behavior of the coatings.

Peeling Strength N/cm2 Anti-corrosive Agent *1 A(St-Bd) SBR A-St PAN EVA - 335 178 262 198 84 X X X X X 1 287 138 238 186 82 o O X X X 2 317 136 173 143 76 o O X X X 3 322 185 244 224 65 o O X X X *1: 1 nitrite type, 2 metaborate type, 3 amine type.

*2: A(St-Bd) acrylic ester modified styrene-butadiene polymer.

SBR styrene butadiene rubber A-St acrylic ester styrene copoiymer PAN polyacrylonitrile emulsion EVA ethylene vinyl acetate copolymer.

Evaluation (i) remarkably flush rust preventing effect O partial rust X no effect or substantially no effect.

As will be seen from the results shown in the Table, it has been found that the styrene-butadiene polymers are the most preferred ones, the essential one of the properties required for the polymer cement mortar, in consideration of its balance against the rust preventing effect.

For the prevention of flush rust it is only necessary to incorporate an anti-corrosive agent in the polymer cement mortar composition or perform a primary treatment on the surface of an object to be coated. Where an anti-corrosive agent is used, it is incorporated in an amount corresponding to about 0.1 to 3.0% by weight, preferably about 0.3 to 1.0% by weight of the composition. Where no anticorrosive agent is used, it is possible to obtain a flush rust preventive effect which is equal to or greater than that obtained with the use of an anti-corrosive agent by performing a primary treatment on the scale-removed surface of an object to be coated with a material prepared by dispersing zinc powder in an epoxy resin or silicate compound, for example.

In this connection, it is needless to say that both of the primary treatment and the use of an anti corrosive agent can be employed as occasion demands.

On the other hand, studies on the aggregates in the polymer cement mortar compositions have resulted in the behaviors of Fig. 3 with respect to the tendency of the bending resistance (f) and compression resistance (C) of the products in terms of the maximum strain (Smax) and the glass content.

From these results it has been found that the glass content of the aggregate in the polymer cement mortar composition has an important effect on the values of fand C and it has been ultimately discovered that the use of an aggregate having a glass content of about 95% by weight or over results in a composition which has the least tendency to crack.

The reason for this resides in the fact that in the case of a granulated blast furnace slag having a high glass content, the material itself exhibits a hydraulic effect.

More specifically, when the granulated blast furnace slag contacts with the moisture in the mortar, minute hydrates (CaO-SiO2. nH2O) are first formed on the surface of the slag and.then a hydrated product (Ca0-SiO2-Al2O3. nH2O) is formed under the action of Al2O3 in the composition in the alkaline atmosphere. It is believed that these hydrated products fill the spaces between the slag particles and serves as a binder thus promoting the hardening. This action is an important chemical feature which is never known in the case of the conventional silica sand and this has the effect of producing a hardened substance which is dense and high in cohesive and adhesive forces.

With the aggregate meeting the thus determined requirements, the particle size of about 0.6 mm or less produces the desired effects from the working property point of the polymer cement mortar composition.

While the aggregate having a glass content of 95% by weight or over is not limited to any particular type so far as the above-mentioned requirements are met, specifically it may be comprised of a granulated blast furnace slag obtained by quickly cooling the molten slag discharged from a blast furnace.

With the polymer (P) and the aggregate (S) selected in the above-mentioned ways, another important matters are the relation in quantity between the components and as regards the C/S ratio Fig. 4 shows a plot of the behavior of the compression strength (C), the bending strength (f) and the tensile strength (TS) obtained by varying the C/S ratio and maintaining the other conditions within the preferred ranges which are confirmed on the above-mentioned grounds. From the disclosed behaviors it will be seen that a coating layer having well-balanced strengths is produced if the C/S ratio is within the range of 0.40 to 0.65.

Fig. 5 is a graph with plots made by obtaining the data of peeling strength according to the P/C ratio by means of the similar technique. In this case, the peeling strength of a value within a given range is ensured when the P/C ratio is within a range of 0.20 to 0.50. As will be seen from the behavior in the Figure 5, the peeling strength decreases with decrease in the value of the P/C ratio and also any excessive value of the P/C ratio cannot ensure manifestation of the effect corresponding to the addition of the polymer.

In the actual application of the polymer cement mortar, one of the known coating means is selected in accordance with the position, condition, etc., of an object to be coated so that if, for example, the object has a wide-spread plane surface or the object has considerable irregularities or undulations, it is convenient to apply the mortar by spray coating employing a spray gun.

With the constitution described in detail above, the polymer cement mortar composition according to the invention is a polymer cement composition which is excellent in performance in terms of the adhesion to ground or priming, abrasion resistance, waterproof effect, weathering resistance, a impact resistance, chemical resistance, anti-corrosive property, elongation, damping property, thermal shock resistance, etc., thereby fully satisfying the functions required for various applications.

The various properties and effects exhibited by the polymer cement mortar composition according to the invention will now be described by way of the following examples.

Note that the polymer cement mortar compositions of the following examples have the following proportions as the common proportions.

Part by weight Acrylic modified SBR latex (solid content 48%) 20 Portland blast furnace cement 25 Granulated blast furnace slag with glass content of 99% (0.5 mm or less) 55 Water 3 EXAMPLE 1 Test specimens were prepared by coating blast-finished steel plates with a zinc powder containing epoxy resin dispersion to a thickness of 15 to 20 ,um and then spraying thereto a polymer cement mortar composition of the above-mentioned proportions to a thickness of 5 mm.

The thus prepared specimens were cured for 28 days at a room temperature and then subjected to wet-dry cycle test, a slurry immersion test and a natural sea water immersion test over 1 year and an accelerated weathering test over 1 ,000 hours. As will be seen from the following Table, there was no change in the surface condition of the steel plates.

Surface Condition Test Item* External Appearance of Steel Plate Wet dry cycle test Whitened surface Good Slurry immersion test Whitened surface Good Sea-water immersion test No change Good Weathering test No change Good *wet-dry cycle condition: an alternate test with 24-hour cycle comprising a 6-hour immersion in 3% salt water at 400 C, a 6-hour warm-air blasting at 400C and a 12-hour left-to-stand cooling Slurry: a slurry essentially consisting of manures of oxes.

Weathering test: an ultraviolet carbon arc weather-meter was used.

EXAMPLE 2 A polymer cement mortar cement prepared according to the common proportions was applied by spray coating to steel plates, glass sheets, acrylic sheets, wooden plywoods and concretes, cured for 28 days and subjected to a peeling strength measurement. The results are shown in Fig. 6.

As shown in Fig. 7, this peeling strength measuring method is such that a jig 3 is attached with an epoxy adhesive to a coating layer 2 applied and formed on a base 1 and a cut was made in the portion of the coating layer 2 contacting with the jig 3 thereby examining the peeling of the coating layer 2.

From Fig. 6 it will be seen that the polymer cement mortar composition according to the invention has an excellent adhesion.

EXAMPLE 3 A comparative test was performed on polymer cement mortar compositions with respect to the wear resisting tendency of the materials according to the following procedure.

A tire having 12 chains wound thereon was rotated in an atmosphere of -1 00C and the chains were brought into contact with the materials thereby measuring the abrasion thereof. Each test specimen in the form of a 400x 1 50x40 mm molded piece was reciprocated at a rate of 66 reciprocating motions per minute with respect to the tire rotating at 3.3S-1. As schematically shown in Fig. 8, a specimen 4 is abraded due to the contact with the chains and a groove 5 is formed. The determination of this abrasion test utilizes the width (cm2) of the section S of the groove 5 as a measure and the behaviors according to the test time are shown in Fig. 9.

In the Figure 9, the behavior indicated by black triangles represents the polymer cement mortar composition using an aggregate having a glass content of 0%, and the behavior indicated by white circles represents the polymer cement mortar composition using an aggregate having a glass content of 50%. The behavior indicated by black circles represents the polymer cement mortar composition using an aggregate having a glass content of 99%.

It will be seen from the Figure that the polymer cement mortar composition of this invention has a remarkably improved abrasion resistance than previously.

EXAMPLE4 The polymer cement mortar composition was applied by spraying to steel plates (2 mm thick) to different thicknesses.

With n representing the ratio of the coating thickness to the base steel plate thickness, the specimens of n=1 to 4 were caused to vibrate at 500 Hz and their damping performances were examined thereby obtaining the behaviors shown in Fig. 1 0.

While it is generally considered that compositions having loss factors of 0.1 or over in the working temperature range can be advantageously used in the fields of civil engineering and building materials, as will be seen from the Figure 10, where n > 2, the loss factor becomes greater than 0.1 in the range of O to 500C and particularly the value of the loss factor becomes as high as about 0.2 in the range of 20 to 300C.

EXAMPLE 5 Molded forms of 1 60x40x40 mm were made of the polymer cement mortar composition and the relation between the compression and bending stress (Ss) and the strain (Sn) was determined on each of the specimens cured for 28 days. The results are shown in Fig. 11. It will be seen that the elongation is exhibited up to the stress of about 1 ,1 00 N/cm2 and in particular the relation between the strain and the stress up to about 500 N/cm2 becomes substantially linear thus indicating that the material of this class is very easily controllable.

In the Figure, the data of the white marks, C,A and V relate to the compression stress and the data of the black marks , r and V relate to the bending stress. The respective marks represent the repeatedly plotted data by the repeated experiments and these data are considered to have a high degree of reproducibility.

EXAMPLE 6 Molded forms of 1 60x40x40 mm were made of the polymer cement mortar compositions using aggregates having glass contents of 99% and 0%, respectively, cured for 28 days and subjected to an cyclic thermal test with one cycle comprising a 6-hour period at 800C and 14-hour period at 50C. The resulting dimensional changes 8 were measured and Fig. 12 shows a plot of the program of the thermal cycle and the dimensional changes 8.

It will be seen that the one having the glass content of 99% is small in dimensional change or high in dimensional stability as compared with the other (the dot-and-dash line) having the glass content of 0%.

Claims (6)

1. A polymer cement mortar composition including a cement (C), an aggregate (S), and a polymer (P), wherein said aggregate has a glass content of 95% by weight or over, said polymer is a styrenebutadiene polymer, and wherein the weight ratios C/S and P/C are respectively 0.4 to 0.65, and from 0.2 to 0.5.

2. A composition according to Claim 1, wherein said aggregate comprises granulated blast furnace slag.

3. A composition according to Claim 2, wherein said granulated blast furnace slag has a glass content of 99% by weight.

4. A composition according to any preceding Claim, wherein said styrene-butadiene polymer comprises a styrene-butadiene polymer or an acrylic modified styrene-butadiene polymer.

5. A composition according to any preceding Claim which comprises from 0.1 to 3% by weight, based on said composition, of an anti-corrosive agent.

6. A composition according to Claim 1 and substantially as hereinbefore described with reference to any of the Examples.