Development of surface repair materials

Vít Petranek¹,

¹Institute of Technology of Building Materials and Components, Faculty of Civil Engineering,

Brno University of Technology, Brno, 602 00, Czech Republic, petranek.v@fce.vutbr.cz,

Summary

One of the reasons for the use of waste materials is decreasing amount of suitable non-renewable raw materials for production of building materials in some areas. The paper describes the issue of utilization of industrial waste materials, namely waste foundry sand and blast furnace slag as fillers to epoxy resin-based repair materials for concrete structures. These repair materials are supposed to be used for reinforced concrete structures. One of the advantages of these materials is also lower price in comparison to produced materials with similar properties. The most important contribution of these materials is from the point of view of the environment. Waste materials are saving natural sources, which could be spared for more convenient use. Also the use of waste materials is reducing load to the environment. The paper describes development of protective and repair materials for reinforced concrete structures.

KEYWORDS: concrete rehabilitation, polymer materials, waste materials.

1. Introduction

The length of life cycle of reinforced concrete construction is significantly influenced by the corrosion factor of concrete and particularly of the reinforcement. Highly developed concrete corrosion can cause concrete structures breakdown.

Concrete can be eroded by invasive fumes and vapors, aggressive waters and solutions, some solid substances, sometimes by the impact of biological factors. Concrete protection can be divided into two parts:

- primary protection

- secondary protection

By primary protection we mean especially concrete mixture quality improvement, concrete consistence, suitable part selection and so on.

By secondary concrete protection we mean measures, which are made after pouring of concrete. For example: painting, toppings, repair material, which will cut down the impact of aggressive materials to a structure. It is possible to implement these measures at later stage of construction stage or after several years from conclusion of construction.

By far the most significant of steps in successful concrete structure repair is the well-performed step of survey of structure and then following choice of optimally designed rehabilitation technology including surface treatment. For survey of damaged concrete structures a methodology has been developed. In case of atmospheric corrosion, especially for CO₂ attack, a damage classification and common suggestions for minimum measures for concrete rehabilitation construction has been developed by our institute.

Surface mending. The aim of using of repair materials is to mend the surface of reinforced concrete structure elements to its the original shape, respectively to reinstate or to make the cover layer over reinforcement thicker. Repair material serves above all to maintaining of longevity of reinforced concrete elements and to reinstatement of its original appearance.

For secondary concrete protection materials based on polymers are mostly used, namely epoxy resins. Disadvantage of the use of these materials is their cost. For cost effective repairs the use of waste materials as fillers to polymers should be considered. An advantage of usage of waste material as fillers for repair materials is the use of industrial waste and therefore its subsequent liquidation. By the same token mineral resources are protected. Mining and processing negatively effects the environment.

The requirement of property of epoxy concrete material is adhesiveness to the base material and firm hold. Good bonding can be achieved only when the original surface is properly prepared and correct preparation of the base is made for achieving the best possible adhesion - minimally 1,5 N/mm². Prepared surface must be solid, load bearing, homogenous, well joined with load bearing construction, dust free, grease free and free of all other impurities, which might act as separator, without bigger pores as well. Further must be without raising dampness. Advantage is a dry base with maximum residual dampness to 4 %. In an opposite case, special material suitable for damped base must be used. As an example of such a material, epoxy resin LENA P102, made by Lena Chemical Ltd., Czech Republic can be used. This type of epoxy resin is possible to apply to a damp base and is possible to use even for underwater jobs.

2. Materials Used for Preparation OF New Repair Materials

2.1 Waste Materials - Fillers

Granulated blast furnace slag: Slag is created by rapid cooling down of molted liquid slag, which is a by-product in production of iron in blast furnaces. The quicker is the process of cooling down, the more of glassy substance is contained in slag and slag is power richer, it means more reactive. Slag is characterized by ratio of glassy and crystallic substance, chemical and mineralogical composition. For the use as a filler granulated blast furnace milled slag has been chosen, produced by a company Trinecke Zelezarny, modified by a company Kotouc Stramberk Ltd., Czech Republic. (Bulk density) Specific weight 2850 kg/m³, specific surface 388,7 m²/kg, dampness 0,02 %.

Figure 1,2. Images show milled blast furnace slag grains enlarged by scanning electron microscope (enlarged 520 x), (enlarged 1500 x)

Foundry sand: Foundry siliceous sand is foundry by-product, where clean siliceous sand for better strength is mixed with e.g. bentonide, water glass, or with mix of these substances or with others substances and then filled into molds. Substance is pressed and mandrel is put in place. After casting, a product is left to cool down. The cast is moved on grate, where the mold breaks up. In a hopper, which is placed below grate, sand is sorted out. Sand is further placed into storage chambers. Foundry sand from a gray foundry UXA Ltd., Brno, Czech Republic has been used. Specific weight 2580 kg/m³, dampness 0,13 %.

Figure 3. Optical microscope image shows foundry sand grains (enlarged 40 x)

2.2 Raw Material - Fillers

Siliceous sand: Siliceous sand has been used as filler to the referential mixture. Commercial standard sand has been supplied by a company GEBRUDER DORFNER GmgH, ISG mbH, Scharhof 1, D 922 42 Hirschau, Germany. Siliceous sand DORSILIT contains more than 98 % SiO₂. Sand is several times washed and properly sorted out to gain over more than twelve varieties. Sand is free of impurities and particles are of round shape. Mixture ISG A1 used has grading of 0,06 – 1,5 mm. Field of application - filler for polymer concrete, for production of plaster mixtures, filler for self leveling floor mixtures, for glue production, for pointing mixtures, for topping mixtures. Physical chemical property - chemical characteristic: silica of white- gray color, dampness 0,01 %, specific weight 2 650 kg/m³.

Figure 4. Optical microscope image shows siliceous sand ISG A1 grains (enlarged 40 x)

2.3 Bonding Agent

Epoxy Resin (ER): Epoxy resin is used for production of paints, glues, laminated plastics, poured and pressed matter and varnishes. Resins have excellent tenacity properties with concrete, ceramics, metals, wood and other materials. Resins are water resistant, alcalic, acid and some solvents resistant, have excellent chemical and electro-insulative properties. Tested epoxy resins used are made by a company Lena Chemical Ltd., Czech Republic and are known under the commercial name Lena P 130. Resin Lena P 130 is made for the usage in manufacture of polymer concretes. Mixture is low viscosity, consists of two parts, and is no solvent mixture. Scope of usage - for mixtures used for polymer-concrete flooring in areas of heavy traffic in industrial halls, repair shops, storages and so on. Specification: workability at 20 ⁰C cca 20 minutes, crushing strength 90 N/mm², tensile strength 53 N/mm², flection strength 93 N/mm².

3. Work Sequence

Repair mixtures have been design with waste material fillings and one referential (non - waste) mixture recommended by company Lena Chemical Ltd., Czech Republic has been chosen. Referential and newly designed mixtures have been examined using basic quality tests – tenacity, compressive strength, tensile strength in bend.

Based on these examinations suitable mixtures have been chosen for further checking. Further supplementary examination have been carried out-water tightness, absorbability, grindability, frost resistance, module of elasticity in bend, UV radiation tolerance and vapor of and carbon dioxide permeability. Not all types of tests and quality requirements for concrete construction rehabilitation are mentioned in specifications. Association for Rehabilitation of Concrete Structures issued publication detailing the type of tests, methodology of tests and minimums requirements for materials used in field of concrete construction rehabilitation. This publication "Technical Conditions for Concrete Construction Rehabilitation" (Drochytka et al. 2003) substitutes specifications and repair materials with waste material fillers must fulfill minimum requirements - see table below.

Figure 5. Images of test beams

Parameter	Conclusive test	Control test
	Required value	Required value
Compressive strength	> 25 N/mm^2 < 50 N/mm^2	> 25 N/mm^2 < 50 N/mm^2
Tensile strength in bending	> 5,5 N/mm^2	> 5,5 N/mm^2
Cohesion with base (without adhesive bridge)	average > 1,7 N/mm^2 individually > 1,5 N/mm^2	average > 1,1 N/mm^2 individually ³ 0,8 N/mm^2
Shrinkage	< 0,5 ^0/00	--
Crack inclination	1 crack of width to 0,1 mm	1 crack of width to 0,1 mm
Frost resistance	T 100	--
Coefficient of thermal expansivity	< 14 x 10^-6	--
Statistical module of elasticity	< 30 GPa	--

Table 1. Required characteristics of repair materials according to Technical Conditions for

Concrete Construction Rehabilitation (Drochytka et al. 2003)

4. Selected results of testing

4.1 Determination of Tenacity – specification Czech standard CSN 73 2577

The essence of tenacity test is determination of force needed for separation of repair mortar from define area from a base using perpendicular movement.

Table 2. Mixture contents and results gained from tenacity tests

Mixture	Content ER [%]	Content and filler type [%]	Tenacity
			[N/mm^2]	Tear off place
130-m	14,3	85,7 siliceous sand	4,23	in concrete
10-m	20,0	80,0 foundry sand	3,17
11-m	22,5	77,5 foundry sand	4,27
12-m	25,0	75,0 foundry sand	3,13
16-m	27,5	72,5 slag	3,77
17-m	30,0	70,0 slag	3,53
18-m	32,5	67,5 slag	3,13

According to Technical Conditions for Concrete Construction Rehabilitation (Drochytka et al. 2003) the required value of tenacity of repair materials is > 1,5 N/mm² and average > 1,7 N/mm², to what all tested mixtures complied.

4.2 Tensile Strength in Bend, EN ISO 178 and Compressive Strength, EN ISO 604

Table 3. Contents of mixtures and results gained from tensile strength tests in bend and compressive strength tests

Mixture	Content ER [%]	Content and filler type [%]	Tensile strength in bend [N/mm^2]	Compressive strength [N/mm^2]
130-m	14,3	85,7 siliceous sand	33,00	59,70
10-m	20,0	80,0 foundry sand	13,65	28,95
11-m	22,5	77,5 foundry sand	17,55	33,13
12-m	25,0	75,0 foundry sand	18,75	34,30
16-m	27,5	72,5 slag	39,30	69,68
17-m	30,0	70,0 slag	39,60	72,34
18-m	32,5	67,5 slag	40,50	75,93

According to Technical Condition for Concrete Construction Rehabilitation (Drochytka et al. 2003) required value of tensile strength in bend of repair materials is > 5,5 N/mm², all tested mixtures complied. For compressive strength test the required value is > 25 N/mm² and < 50 N/mm². All examined mixtures complied with the minimum value. As far as the maximum value of 50 N/mm² is concerned, this value is needed for silicate materials for reason, that the repair material should not have grater module of elasticity than the base material. Polymeric composites have generally lower module of elasticity and tested mixtures have reached values of elasticity module bellow 5 GPa (see below), therefore it is impossible to take the compressive strength test of 50 N/mm² as being of maximum value.

4.3 Water Tightness Determination, specification Czech standard CSN 73 2578

The essence of this test is to determine amount of water, which will be absorbed by the tested sample during given time, after 30 minutes.

Table 4. The amount and type of filler influencing water tightness

Mixture	Content ER [%]	Content and filler type [%]	Water tightness [l/m^2.30min]
130-m	14,3	85,7 siliceous sand	0,00
11-m	22,5	77,5 foundry sand	0,00
16-m	27,5	72,5 slag	0,00

Gained values show hundred percent water tightness of all mixtures after the elapse of given time. Thanks to epoxy resins, which perfectly coats filler grains, the material does not show any open pores and water cannot diffuse into tested material.

4.4 Absorption Determination, specification Czech standard CSN 72 2448

Absorbability is defined as water quantity, which is absorbed by dried sample into his cavities and pores when submerged in water.

Table 5. Quantity and type of filler influencing absorbability

Mixture	Content ER [%]	Content and filler type [%]	Absorption [%]
130-m	14,3	85,7 siliceous sand	0,20
11-m	22,5	77,5 foundry sand	0,20
16-m	27,5	72,5 slag	0,01

Figure 6. Influence of filler type on absorbability test

From gained values is perceptible, that the least, virtually - zero absorbability, show mixtures containing blast furnace slag. Mixtures containing siliceous sand ISG A1 and foundry sand have values 20x higher. It is caused by pores and cavities, which occur on the surface of tested samples and are caused by imperfect coating of material grains of filling by epoxy resin on the surface of the sample on the contact area with the mold. When the test of absorbability is performed, water gets into pores and cavities, therefore these mixtures show some percentage increase in weight of water. Mixtures made out of blast furnace slag do not show pores and cavities.

4.5 Frost Resistance, specification Czech standard CSN 72 2452

Frost resistant mortars are tested by alternate freezing and defreezing of tested samples water saturated. One freezing cycle consists of at least four hours of freezing at temperature - 20 ± 3 ⁰C and at least two hours of defreezing in water bath with temperature about 20 ± 3 ⁰C. Tested samples were subjected to 100 freezing cycles. Then tensile strength test in bend and compressive strength tests have been carried out.

Table 6., 7. Mixture contents and frost resistance tests results (after 100 freezer cycles)

Mixture	Content ER [%]	Content and filler type [%]	Compressive strength [N/mm^2]
			Before examination	After exam.
130-m	14,3	85,7 siliceous sand	59,70	57,38
11-m	22,5	77,5 foundry sand	33,13	29,88
16-m	27,5	72,5 slag	69,68	69,13

Mixture	Content ER [%]	Content and filler type [%]	Tensile strength in bend [N/mm^2]
			Before examination	After exam.
130-m	14,3	85,7 siliceous sand	33,00	31,50
11-m	22,5	77,5 foundry sand	17,55	15,25
16-m	27,5	72,5 slag	39,30	39,30

strength before frost resistance tests

strength after frost resistance tests

Figure 7.,8. Image showing influence of filler type at frost resistance test

According to Technical Condition for Concrete Construction Rehabilitation (Drochytka et al. 2003) repair material must comply with 100 freezing cycles. This requirement has been fulfilled by all tested mixtures.

4.6 Module of elasticity in bend, EN ISO 178

Table 8. Mixture contents and resulting values of module of elasticity in bend

Mixture	Content ER [%]	Content and filler type [%]	Module of elasticity in bend [GPa]
130-m	14,3	85,7 siliceous sand	4,861
11-m	22,5	77,5 foundry sand	2,948
16-m	27,5	72,5 slag	2,857

Figure 9. Image showing influence of filler type on module of elasticity in bend

According to Technical Conditions for Concrete Construction Rehabilitation (Drochytka et al. 2003) module of elasticity in bend of repair material must have value < 30 GPa. All tested mixture fulfilled this requirement.

4.7 UV Radiation Tolerance Determination, specification Czech standard CSN 67 3091

Table 9., 10. Mixture contents and resulting values gained from UV radiation tolerance tests (after 250 hours)

Mixture	Before examination
	Tenacity [N/mm^2]	Tear off place	Color	Cracking, peeling
130-m	4,23	in concrete	gray with shine	none
11-m	3,27		black with shine
16-m	3,77		gray-greenish with shine

Mixture	After examination
	Tenacity [N/mm^2]	Tear off place	Color change	Cracking, peeling
130-m	4,06	in concrete	turning yellow with shine	none
11-m	3,23		without changes
16-m	3,74		turning yellow with shine

From tables 9, 10 follows that epoxy resins even when mixed with waste material fillings show after tests of UV radiation tolerance excellent tenacity properties. Tested mixtures were subjected UV radiation for a period of 250 hours. Cracking and peeling of material has not developed, only change, after exposing of materials to UV radiation, has been change in color. Samples with foundry sand have not shown any changes in color, whereas siliceous sand ISG A1 and blast furnace slag materials caused color change-samples turned yellow.

5. CONCLUSIONS

By comparing tests on trial samples of individual mixtures with values mentioned in publication Technical Conditions for Concrete Construction Rehabilitation (Drochytka et al. 2003) is possible to conclude, that mixtures of waste materials fulfill and in some aspects significantly surpass required values.

Characteristics of newly developed epoxy resins repair materials especially with blast furnace slag surpass properties of mixtures using siliceous sand.

The possibility of usage of waste material as fillers for epoxy repair materials in the area of concrete construction rehabilitation has been shown.

Usage of these materials is profitable in the light of decreased monetary expense on the production of epoxy concrete repair plasters.

The most important aspect however is ecological standpoint - it saves non-renewable sources of high quality siliceous sands which are used e.g. for production of Czech glass. Estimated deposits of high quality glass sands in Czech Republic are estimated to last only for max. 15 years. Indispensable positive element is also the usage of industrial wastes, which is continuing to rise in quantity every year.

Development of above mentioned mixtures containing waste materials as fillers is still in progress. Materials meet requirements of main document in the Czech Republic, Technical Conditions for Concrete Construction Rehabilitation (Drochytka et al. 2003) and search for other test and its implementation required by EU standards is also in progress.

References

1. Michalcova, G.. Modification of Epoxy Screed and Repair Materials with Waste Fillers, Graduation thesis. Brno University of Technology, Brno 2003.

2. Drochytka, R. & Dohnalek, J. & Bydzovsky, J. & Pumpr, V.. Technical Conditions for Concrete Construction Rehabilitation, Bekros Brno 2003. ISBN 80-239-0516-3

3. EN ISO 178 Plastics - Determination of flexural properties

4. EN ISO 604 Plastics - Determination of compressive properties

5. Czech standard CSN 67 3091 Laboratory tests of resistance of paint coatings in atmospherical conditions

6. Czech standard CSN 72 2448 Testing of moisture content and absorptivity of mortar

7. Czech standard CSN 72 2452 Testing of frost resistance of mortar

Acknowledgement

This paper was prepared with financial support from the research project CEZ - MSM 0021630511, entitled: “Progressive Building Materials with Utilization of Secondary Raw Materials and their Impact on Structures Durability” and research project FT-TA 5/092 „Complex surface system offlors with utilization of by-products.”