developments in epoxy modified portland cement...

Developments in EpoxyModified Portland Cement Mortars

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Developments inEpoxy ModifiedPortland CementMortars

technical report

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DEFINITIONSPolymer Cements (PC) - a general term indicatingany polymer containing product used as an adhesiveor mortar or screed. The term is mainly used forproducts containing polymer plus non-reactive fillere.g. epoxy/sand.

Polymer Modified Portland Cement (PPC) -products based on traditional inorganic Portlandcement as the main binder, with the addition ofemulsion polymer to act as an improver orwaterproofing agent. (Typically PVA, SBR or acrylic).

Epoxy Portland Cement (EMC) - these are PPC’s inwhich the emulsion polymer has been replacedby an epoxy/hardener copolymer system i.e. as withIncorez 148/010.

ADVANTAGES OF EMC OVER PPCi) Superior strength properties (typically twice the

compressive strength of PPC).ii) Increased chemical resistance - particularly

towards mineral acids.iii) Reduced sensitivity to polymer rewetting, which

can cause swelling/disbondment.iv) Reduced drying shrinkage cracking enabling the

omission of curing membrane and improved tolerance to hot dry climates.

v) Excellent adhesion to damp/old concrete without the need for primers.

DISADVANTAGES3 component packaging although there is potential toreduce this to 2-component or even 1-component byuse of “dry” liquid technique.

APPLICATION AREASi) Thin screeds or toppings requiring high strength

e.g. floor toppings in abattoirs, factory decking, marine applications.

ii) Damp cellars to reduce the ingress of water from external sources.

iii) Repair of tanks or reservoirs where permanent contact with water occurs.

iv) Flooring screeds in the hygiene and food industries or wherever chemical resistance is important e.g. sewage treatment plant.

v) To reduce solvent based systems in enclosed areas, which have little or no ventilation.

CHOICE OF EPOXY/HARDENERHardenerThe following grade is recommended:Incorez 148/010

This product has been chosen for its specificcharacteristics:

a) Low viscosity, confers excellent workability. b) Excellent emulsion stability in a cement rich

environment. c) Synergistic curing properties with Portland cement. d) Long pot life.

Epoxya) Normal liquid grade (DER353, Epikote 215) b) Solid epoxy emulsion (Beckopox EP384)

FORMULATING TIPSSuperplasticiser - these are used to increase theworkability of cement pastes and should be added insmall doses to the EMC formulations. A naphthalenesulphonate type is recommended.

Water/cement ratio - affects the strength propertiesdramatically in all PPC and EMC formulations andshould be calculated to yield values <0.6 whereverpossible.

Graded Silica Sand - a selection of graded silicasands are chosen to achieve a close packed, densestructure. Only washed, dry, graded silica sandshould be used.

Mixing Techniques - the hardener/epoxy should bemixed thoroughly at the outset and placed in thecement mixing container. The dry powder(cement/sand) blend should then be added to theemulsified epoxy, slowly. A drill/paddle can be usedfor mix quantities up to 10kg.

The last twenty years has seen a wide acceptance of POLYMER MODIFIED PORTLAND CEMENT systems,mainly based on emulsions of thermoplastic polymers such as poly(styrene-butadiene) (SBR) and poly(acrylic-esters) (PAE). The first UK Patent applied for however was in 1923 by Cresson1 in which natural rubber was inan cementitious paving system. Since then a wide variety of applications have been made including bridgerepairs, car parking, ship decking and flooring. According to statistics, some countries are producing over40,000 tons p.a. of polymer concrete.

The use of thermoplastic emulsions is claimed to improve a variety of mortar properties including strength,waterproofness and adhesion. Strength (compressive, tensile, flexural) is often improved indirectly, sincewater:cement ratio (w/c) can be reduced due to the improved workability found with emulsion polymer.Normally, however, the direct addition of emulsion resin to a mortar will reduce the mortars compressivestrength unless a calculated reduction in w/c is made.

Improvements to the strength characteristics of mortar are seen as a major benefit to using polymer modifiedsystems; particularly since Portland cement compositions are weak in tension compared to other buildingmaterials, see table 1 below.

KEY

a Values depend on water:cement ratios, figures quoted are for 0.81 and 0.41 water:cement ratios.

b Values depend on water:cement ratios as in a, tensile is about 8% of compressive strength.

c Aluminium type 1100 as defined by the Aluminium Alloy Designation, USA.

d Figures quoted are for strengths perpendicular to the grain.

e Compressive strength is generally taken as being equal to tensile strength.

1 Cresson L: British Patent 191, 474, 12 Jan (1923)

Developments in Epoxy ModifiedPortland Cement Mortars

technical report

Concrete

Steel, Construction

Aluminium (type 1100c)

Oak, redd

Polystyrene, high impact

ABS, medium impact

SG

2.2-2.4

7.7-7.83

2.55-2.80

0.64-0.71

0.98-1.10

1.01-1.15

Compressive Strength, MPa

14-40 a

350-400 e

90-160 e

7.1

-

-

Tensile Strength, MPa

1.1-3.3 b

350-400

90-160 e

5.3

14-45

16.63

Modulus of Elasticity, MPa

20,700-34,500

180,000-207,000

73,000

12,500

1,750

2,000-3,000

table 1 strength properties for some building materials

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In an ideal situation cementitious repair mortars, for instance, should possess similar strength properties tobase concrete. This is not easy to achieve since it is difficult to compact mortar and impossible to incorporatesteel reinforcement except possibly as fibres. The use of polymers is therefore claimed to be advantageous. It is unfortunate, however, that the type of emulsion polymer in use, by virtue of its physio-chemical structure,reduces in strength dramatically when rewetted. Unmodified mortar actually shows an increase in strengthwhen immersed in water, see table 2 below.

This ability to reabsorb water, after curing, is a common feature of many emulsion polymers. This characteristicmay, however, have dramatic consequences in practice and can sometimes be the underlying cause ofdisbondment, for example, when polymer modified flooring screeds are applied over damp concrete. Table 3below indicates typical water absorption values for emulsion polymer films cast at 100 microns thickness andallowed to cure for one month at 20ºC.

*BIS A/F, Incorez 148/010 curing agent

table 2 effect of water absorption on compressive strength of latex modified mortars

polymer-cement ratio. 20% dry wet

300

200

150

100

50

250

com

pre

ssiv

e st

reng

th k

g/cm

2

types of mortar

Un modified

SBR-1 modified

SBR-2 modified

PVDC-1modified

PVDC-2modified

NBRmodified

CRmodified

PAE modified

PVAC modified

Water

17.75

18.35

1.25

Reagent5% w/w hydrochloric acid

8.41

8.04

2.53

table 3 % weight increase after immersion

Polymer type

PAE

SBR

EPOXY*

5


technical report

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The theoretical principals governing the strength of cement composites have been well documented and arerelated to two major influences

1) Improvement in the cement / aggregate bond

The strength of ordinary mortar and concrete depends to a large extent on the strength of the aggregate-to-cement paste bond. It has been shown by Alexander2 et al. that this bond strength is lower than the cementpaste bond strength. Because of this, initial cracking usually develops at the aggregate paste interface ratherthan in the paste itself. Given their adhesive nature, certain emulsion polymers have a potential to improve theaggregate to cement paste bond strength.

2) Reduction of stress in the vicinity of crack tips

The difference between theoretical and observed strengths in brittle materials is theresult of the presence of flows or cracks in the composite. This theory was postulated byGriffiths3 in 1920 and later applied to concrete by Kaplan4 and Glucklich5. According toGriffiths the presence of cracks initiates fracture as a result of high stress concentrationsinduced at, or near to, the crack tips when the material is loaded. The Griffiths equationis given as:

Where ‘σ is the applied tensile stress, ‘T is the specific surface energy, ‘E is the modulus of elasticity and ‘C is the length of the crack.

Hence lower strength is to be expected when longer cracks or discontinuities are present.

A further desirable requisite is to improve chemical resistance. Polymer modified Portland cement mortarsgenerally have good resistance to alkalis, fats and oils but poor resistance to acids, sulphates and somesolvents. Achieving these improvements would permit the use of polymer cements into application areas whichare currently dominated by wholly organic resin composites, such as the epoxy/sand screeds for the chemicaland sewage industry.

Waterbased Epoxy

One opportunity that has presented itself to Incorez has been the use of water borne epoxy polymers toupgrade Portland cement mortars in those areas outlined above. Water borne epoxies and more importantlythe use of an appropriate curing agent, have rarely featured as polymer additives in Portland cementtechnology. Some data exists, particularly in the USA, for applications and test work carried out notably byMcClain6. Other systems, mainly in Europe, have tried to adopt existing coatings resin technology with littlesuccess. Many of the curing agents in particular are too viscous, or produce unworkable mortars. Some epoxysystems are incompatible in a cement environment, where calcium ions cause precipitation of the resinemulsion. Nevertheless epoxy polymers, since they exhibit high adhesive and tensile strength are morechemically resistant than say acrylics, should prove to be advantageous in mortar compositions.

2 Alexander KM, Wardlow J and Gilbert DJ: Aggregate-Cement Bond, Cement Paste Strength and the Strength of Concrete, Proc. Conf. Structure of Concrete and Its Behaviour Under load, London (1965), 59, Cement and Concrete Association, London (1968)

3 Griffiths AA: The Phenomena of Rupture and Flow in Solids, Phil. Trans, Ray Soc. A, 221,163 (1920)

4 Kaplan MF: Crack Propagation and the Fracture of Concrete, J. Am. Concrete Inst., 58, 591, (1961)

5 Glucklich J : On the Compression Failure of Plain Concrete, Theoretical and Applied Science Rep., No. 215, University of Illinois (1962)

6 McClain RR: Epoxy-Modified Cement Admixtures, Proceedings of Second Int. Congress on Polymers in Concrete, University of Texas, Austin, 483 (1978)

2 E Tπ C

σ=

7

In our development work two cementitious systems were examined:

i) a thin topping or thick coating, ref. EMC-3ii) a 10mm self levelling screed, ref. PF-2

Formulations are outlined below. It must be remembered that both formulations are simplistic in design and donot include fibres or microsilica, both of which would improve strength and resistance properties markedly. Theaim was merely to assess the influence of the polymer component rather than the cementitious mix design.

Guide Formulation for PF-2Description

Epoxy modified cement floor screed, 10-25mm thicknessfor use in warehouse, cellars and industrial applications.Application by spiked roller or pump.

FORMULATION

PART A % by weight

Silica sand (1.1-2.3mm)


Silica sand - Redhill 65

Rapid hardening cement

Pulversied Fuel AshPozzolan

Plasticiser (naphthalenesulphonate eg. Sikament)

Quartz Aggregate (2-3mm)

22.24

18.85

3.77

22.66

7.54

0.75

11.36

Supplier

Various

Various

Sibelco

Blue Circle

PozzolanicLytag

Sika

Bush Beach

Incorez 148/010Water

1.3910.05

Incorez

PART C

PART B

Epikote 215

Total

1.39

100.00

Momentive

INSTRUCTIONS FOR USE

Mix parts B and C. Add half to the power mixer followedby Part A. Add the remainder of parts B and C after oneminute. After mixing, deposit flowing mixture onto floorand place/deareate with spiked roller.

DATA

Mix ratio= 6.8 : 1 (Part A: Parts B and C)Water/cement= 0.45% polymer by weight cement= 11.04%Working Life = circa. 1 hour at 200C

Guide Formulation for EMC-3Description

Epoxy/cement waterproof coating, application thickness1mm. For use in cellars, tanking and generaldamproofing work.

FORMULATION

PART A

MIX

% by weight

Silica sand-Redhill 110

Pulverised Fuel AshPozzolan

Ordinary Portland Cement

Hydrated Lime (Limbux)


39.15

14.07

23.50

1.55

1.50

Supplier

Sibelco

PozzolanicLytag

Blue Circle

Pozzolanic Lytag

Sika


3.3613.50

Incorez

PART C

PART B

Epikote 215

Total

3.36

100.00

Momentive

DATA

Mix ratio= 3.9 : 1 (Part A: Parts B and C)Water/cement= 0.596% polymer by weight cement= 25.55%Compressive Strength = circa. 30N/mm2 (28 Days)Working Life = circa. 1 hour at 200C


technical report

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A variety of tests were carried out on the cementitious formulations incorporating the aqueous epoxy. Control

samples were also prepared using traditional thermoplastic emulsions based on SBR and PAE. A summary of

these tests is given in the following tables:

Compressive Strength - N/mm2

Flexural Strength - N/mm2

Slant Shear Adhesion - N/mm2

Ref. PF-2 Strength Test (BS6319)

28 days

9.58

10.84

37.50

43.10

Polymer Modification

Poly(styrene co-butadiene)

Incorez 148/010 + Epoxy

1 day

12.10

21.60

7 days

43.90

57.10

28 days

50.72

59.80

1 day

1.20

1.35

7 days

5.78

6.16

Compressive Strength - N/mm2

Flexural Strength - N/mm2

Slant Shear Adhesion - N/mm2

Ref. EMC-3 Strength Test (BS6319)

28 days

8.15

9.31

18.50

46.50


Poly(styrene co-acrylate)(Acronal S702)


1 day

0.00

4.40

7 days

14.00

21.00

28 days

18.10

45.30

1 day

-

1.82

7 days

2.57

4.94

1 Day 7 Days 14 Days 28 Days 56 Days

Ref. PF-2 Shrinkage - Expressed as % Change of Original Length


Poly(styrene co-butadiene)


0.05

0.05

0.08

0.08

0.09

0.08

0.092

0.104

0.015

0.125

1 Day 7 Days 14 Days 28 Days 56 Days

Ref. EMC-3 Shrinkage - Expressed as % Change of Original Length


Poly(styrene co-acrylate)


0.00

0.07

0.02

0.08

0.075

0.180

0.102

0.228

0.120

0.245

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Discussion

Strength PropertiesDramatic improvement in compressive strength is observed for EMC-3 formulations based on water borneepoxy almost 2.5 times the value of an acrylic emulsion modification. Less dramatic results are observed withPF-2 formulations, since the polymer content is lower and this has less of an influence in the system. Flexuralstrength is marginally higher for both cementitious products by about 14% in comparison to ordinary emulsionsystems. Slant sheer adhesion prisms all showed cracking within the mortar rather than at the interface,illustrating a high level of adhesion to old concrete.

Workability / Pot lifeThe epoxy modified systems showed only a slight reduction in workability compared to the emulsion polymers.For instance, using a flow table (BS 4551:1980), the epoxy system, EMC-3, gave a reading of 215mm against225mm for the styrene acrylic. This was measured 1hr after initial mixing. Pot life was assessed asapproximately 90 minutes for the epoxy cement and 120 minutes for the styrene acrylic.

Linear ShrinkageTests carried out to ASTM C82782 showed shrinkage with the epoxy modification to be higher than thecontrols. The levels are quite small, however, when compared to say epoxy/sand screeds with shrinkage ofca.2%. Shrinkage in the epoxy cement system is a result of chemical crosslinking, whereas standard. emulsionpolymers physically coalesce to form a loose network in the cement matrix. It is essentially the chemicalcrosslinking of the epoxy which gives rise to a more intricate and ordered polymer structure in the cementcomposition. This also accounts for the improvements in mechanical properties.

Chemical ResistanceThis property was assessed by two methods,

i) By wt. changeii) By change in compressive strength

In both cases samples were immersed in a variety of reagents for one month, at 200C, prior to testing.Reagents used were:

Water 5% Sulphuric acid 5% Sodium hydroxide 5% Sodium hypochlorite 5% Sodium chloride 5% Non-ionic surfactant

Results showed that weight changes experienced by the epoxy system were much lower than those of thecontrols. Overall weight changes were only one quarter to one third of the acrylic mortar. The increased epoxycontent in the EMC-3 formulation gave rise to an overall improved performance in chemical resistanceproperties compared to PF-2. In particular, acid resistance was far superior for the epoxy system, compared tothe acrylic control, values were 0.8% change for the epoxy against 12% change for the acrylic.

Compressive strength tests also showed the epoxy system outperform the standard emulsion controls,although this was likely since initial strength values for the epoxy were higher anyway. In terms of % retentionof original strength the epoxy mortars showed only a 5% improvement.


technical report

10

In summary, the chemical resistance tests showed that whilst the epoxy modification gave improvements overtraditional polymers, permeation of chemicals can still occur, albeit at a slower rate. It has to be borne in mindthat the polymers are strictly secondary binders in the mortars and complete protection of the cement paste bythe polymer is not possible.

Water Retaining Properties

During the course of our experiments with different test methods for compressive strength testing, it was alsoseen that the epoxy system was less sensitive to the conditions under which samples were cured.Thermoplastic emulsion polymers favour a drying out period cure, at 65%RH and hence thicker sections tendto yield lower strength values. In our tests for instance the following results were found:

The ability of the water borne epoxy to synergistically strengthen the cement matrix, particularly in thepresence of water, was also evaluated by studying the tensile strength of pure polymer strips, in which waterhas been included at a level of 25% of the formula wt.

In effect, the epoxy system, by virtue of its crosslinking mechanism, is hardly affected in terms of physicalproperties by the presence of water. The epoxy polymer also demonstrates excellent water retainingproperties. For example, in the above tests small weighed pieces of cured polymer were placed in an oven at1000C for 4 hrs. After this period samples were reweighed and water loss was observed to be only 2.6%. Thisis a property of high potential value, particularly in hot countries, where loss of water by surface evaporationcauses major problems in application, particularly manifested by drying shrinkage cracking.

Sample

Incorez waterborne epoxy

Incorez waterborne epoxy + 25% water

Acrylic

S.B.R.

Tensile Strength N/mm2

18.6

16.9

1.4

0.9


Acrylic


Compressive Strength N/mm2

50mm

Cube

14.0

21.0

70.7mm

Cube

2.0

13.5

7 Day Compressive Strengths

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Further Work

In view of the increasing trend to employ solid epoxy emulsions a series of tests were conducted using thissystem, as given in formulations PF-4 and EMC-4 below. The most notable points were:

a) Compressive strength values were between 80-90% of the corresponding liquid epoxy formulations. b) Workability was virtually equal to the control emulsions (SBR, PAE).

Conclusion

The foregoing research has illustrated how new and improved polymer modified Portland cement mortars,based on water borne epoxy technology, can extend the already widening market for cement products. Inparticular, high strength mortars can be easily achieved which are less prone to varience under differentconditions of humidity and thickness of section. There is also an additional benefit in that the strong waterretention properties of the epoxy/curing agent will reduce the tendency for drying shrinkage cracking to occur.

Guide Formulation for PF-4Description

Epoxy modified cement floor screed, 10-25mm thicknessfor use in warehouse, cellars and industrial applications.Application by spiked roller or pump.

FORMULATION

PART A % by weight



Silica sand - Redhill 65

Rapid hardening cement

Pulversied Fuel AshPozzolan


Quartz Aggregate (2-3mm)

22.24

18.85

3.77

22.66

7.54

0.75

11.36

Supplier

Various

Various

Sibelco

Blue Circle

PozzolanicLytag

Sika

Bush Beach


0.708.73

Incorez

PART C

PART B

3.40

100.00

Cytec

INSTRUCTIONS FOR USE

Mix parts B and C. Add half to the power mixer followedby Part A. Add the remainder of parts B and C after oneminute. After mixing, deposit flowing mixture onto floorand place/deareate with spiked roller.

DATA

Mix ratio= 6.8 : 1 (Part A: Parts B and C)Water/cement= 0.45% polymer by weight cement= 11.04%

Guide Formulation for EMC-4Description

Epoxy modified waterproof coating, application thickness1mm. For use in cellars, tanking and generaldamproofing work. Application by brush or spray gun.

FORMULATION

PART A

MIX

% by weight

Silica sand-Redhill 110

Pulverised Fuel AshPozzolan

Ordinary Portland Cement

Hydrated Lime (Limbux)


39.15

14.07

23.50

1.55

1.50

Supplier

Sibelco

PozzolanicLytag

Blue Circle

ICI

Sika


1.7010.20

Incorez

PART B

DATA

Mix ratio= 3.9 : 1 (Part A: Parts B and C)Water/cement= 0.596% polymer by weight cement= 25.55%Compressive Strength = circa. 60N/mm2

Beckopox EP384

Total

PART C

8.33

100.00

CytecBeckopox EP384

Total

Incorez Limited

Iotech House • Miller Street

Preston • Lancashire

PR1 1EA • England

t: +44 (0)1772 201964

f: +44 (0)1772 255194

e: [email protected]

w: www.incorez.com

Incorez Corporation

79 Bradley Street

Middleton • Connecticut

06457 • USA

t: +1 (860) 613 1613

f: +1 (860) 613 1637

e: [email protected]

w: www.incorez.com

Manufacturers of specialist resins & polymers:

• Oxazolidines

• Waterborne epoxy curing agents

• Polyurethane dispersions

• Polyurethane/acrylic hybrid dispersions

• Polyurethane prepolymers

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