WORLD UNIVERSITY OF BANGLADESH

Course Name: Wet Processing Technology- IICourse Code: TE 801

Assignment onWater Repellency Finishing

Submitted To Submitted ByEngr. Elias Khalil Mirajul Islam (607)

Senior Lecturer Ayesha Islam (611) Department of Textile Engg. Iftekhairul Islam (601)

Gazi Kanita (610)

Department of Textile Engg.

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Date: 10/12/2016Water Repellency Finishing

IntroductionThe definition of water repellent is something that, when exposed to liquid, reacts with the liquid to cause it to move away instead of to be penetrated or soaked in.Finishes that repel water, oil and dry dirt are important in all parts of the textile market- for clothing, home and technical textiles. Water repellency is achieved using different product groups, but oil repellency is attained only with fluorocarbon polymers. They are modified to have a wide range of properties. This is one of the most interesting new developments finishing.

Water Repellency is more difficult to define because various static and dynamic tests are used to measure water repellency. Generally speaking water repellent fabrics are those which resist being wetted by water, water drops will roll off the fabric. A fabric's resistance to water will depend on the nature of the fiber surface, the porosity of the fabric and the dynamic force behind the impacting water spray. The conditions of the test must be stated when specifying water repellency. It is important to distinguish between water-repellent and water-proof fabrics. Water Repellent Fabrics have open pores and are permeable to air and water vapor. Water-repellent fabrics will permit the passage of liquid water once hydro-static pressure is high enough. Water-Proof Fabrics are resistant to the penetration of water under much higher hydrostatic pressure than are water-repellent fabrics. These fabrics have fewer open pores and are less permeable to the passage of air and water vapor. The more waterproof a

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fabric, the less able it is to permit the passage of air or water vapor. Waterproof is an overstatement, a more descriptive term is impermeable to water. A 154 fabric is made water-repellent by depositing a hydrophobic material on the fiber's surface; however. Water proofing requires filling the pores as well.

In addition to the desired repellency effects, other undesirable fabric properties are often found with repellent finishes. These include problems with static electricity, poor soil removal in aqueous laundering, stiffer fabric hand, greying (soil re deposition) during aqueous laundering and increased flammability. Some fabric properties that are often improved by repellent finishes include better durable press properties, more rapid drying and ironing, and increased resistance to acids, bases and other chemicals.

Kinds of textiles OR WR DS SR CF AS H PSport wear, leisure wear + ++

+0 + + + +++ ++

Uniforms, workwear +++

+++

++ +++

+ + ++ +++

Upholstery and automotive fabrics

+++

++ +++ ++ +++

+++

+ +

Awnings, sunblinds, curtain fabrics

+ +++

+++ 0 0 0 0 +

Table and bed linen +++

++ ++ +++

+ 0 + +++

Carpets ++ ++ +++ 0 ++ ++ 0 +Oil repellency + OR, Wter repellency + WR, dry soil = DS, soil release = SR, crockiong fastness = CF, antistatic = AS, handle = H, permanence = p

Mechanism of repellency Repellent finishes achieve their properties by reducing the free energy at fibre surface. If the adhesive interactions between a fibre and a drop of

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liquid placed on the fibre are greater than internal cohesive interactions within the liquid, the drop will spread. If the adhesive interactions between the fibre and the liquid, the drop will not less than the internal cohesive interactions within the liquids are referred to as low energy surfaces. Their critical surface energy or surface tension γc must be lower than the surface tension of the liquid γl (internal cohesive interaction) that is repelled. γl of water, at 73 mN m-1, is two to three times greater than γl of oils (20 – 35 mN m-1 ). Therefore, oil repellency finishes with fluorocarbons (γc = 10-20 mN m-1 ) always achieve water repellency. But fluorine-free products, examples silicones (γc = 24-30mN m-1) will not repel oil. Low energy surfaces also provide a measure of dry soil repellency by preventing soil particles from strongly adhering to fibre surfaces. This low interaction allows the soil particles to be easily dislodged and removed by mechanical action.

There are different ways that low energy surfaces can be applied to textiles. The first way is mechanical incorporation of the water-repellent products in or on the fibre and fabrics surface, in the fibre pores and in the spacing between the fibres and the yarn. Examples of these are paraffin emulsions. Another approach is the chemical reaction of the repellent material with the fibre surface. Example of these are fatty acid resins. Yet anaother method is the formation of a repellant film on the fibre surface. Exampls of these are silicone and fluorocarbon products. The final approach is to use special fabric construction like stretched polytetrafluroethylene films (Goretex), films of hydrophilic polyester (sympatex) and microporous coating (hydrophilic modified polyurethanes).

A

5

A. Hydrophobic interactions; B. polar interactions ; C. Fibre surface

Repellent Chemistry

Praffin repellents

These were one of the earlist water repellents used, but do not repel oil. Typically the products are emulsion that contain aluminium or zirconium salts of fatty acids (usually stearic acid). These materials increase the finish’s adhesion to polar fibre surfaces by forming polar-non-polarjunctions as shown in figure. The paraffinic portion of the repellent mixture is attracted to the hydrophobic regions, while the polar ends of the fatty acids are attracted to the metal salts at the fiber surface. These finishes can be applied both exhaustion and padding. They are compatible with most kinds of finishes but they increase flammability. Although they are available ar relatively low cost and generate uniform waterproof effects, the lack of durability to laundering and dry cleaning and their low air and vapour permeability limits the use of paraffin-based repellents.

A

Figure: Fatty acid metal salts.

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Stearic acid-melamine repellents

Compounds formed by reacting stearic acid and formaldehyde with melamine constitute anther class of water repellent materials. An examples is shown in fig. The hydrophobic character of the stearic acid groups provide the water repellency, while the remaining N-methylol groups can react with cellulose or with each other to generate permanent effects. Advantages of the stearic acid melamine repellents include increased durability to laundering and a full applied by exhaustion procedures. Their use as extenders for fluorocarbon repellents is noe increasingly replaced by boosters as descrived in section.

Silicone water repellents

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Polydimethylsiloxane products that are useful as water repellents con form a hydrophobic layer around fibres. The unique structure of the Polydimethylsiloxane provides the ability to form hydrogen bonds with fibres as well as display a hydrophobic outer surface. In order to agin some measure of durability, silicones designed as water-repellent treatments usually consist of three components, a Silanol, a silane and a catalyst such as tin octoate. The catalyst enables not only moderate condensation conditions but also promotes the orientation of the silicone film on the fibre surface. The outward oriented methyl groups generate the water repellency. During the drying step after pad application, the silanol and silane components con react to form a three-dimensional cross-linked sheath around the fibre. This reaction is often completed after storage of about one day, then providing full repellency. The SI-H Groups of the silane are the reactive links in the silicone chain. Generating crosslinks or being oxidized by air or hydrolyzed by water to hydroxyl groups. These hydroxyl groups may cause further crosslinking. But if too many of them stay unreacted, their hydrophilicity will decrease the repellency.

Components of silicone water repellent:

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Selan

Fig: silanol-silane reaction

Advantage:Advantages of silicone water repellents include a high degree of water repellency at relatively low (0.5-1% ow) on weight of fabric concentrations, very soft fabric hand, improved suability and shape retention, and improved appearance and feel of pile fabrics. Some modified silicone repellents can be exhaust applied (to pressure-sensitive fabrics).

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The disadvantages of silicone repellents include increased pilling and seam slippage, reduced repellency of excessive amounts are applied (for example silicone double layer with polar outside, only moderate durability to laundering (through hydrolysis of Sloane and rupture of the film by strong cellulose fiber swelling) and dry cleaning (adsorption of surfactants) , and no oil and soil repellency. The silicone finish may enhance the attraction of hydrophobic dirt. In addition, the waste water, especially the residual baths, from these finish application processes are toxic to fish.

Fluorocarbon-based repellents

Fluorocarbons (FC) provide fiber surfaces with the lowest surface energies of all the repellent in use. Both oil and water repellency can be achieved. FC repellents are synthesized by incorporating perfluoro alkyl groups into acrylic or urethane monomers that can then be polymerized to form fabric finishes (Fig.6.7). Originally, the perfluoro alkyl groups were produced by electrochemical fluorination, but today they are produced by telomerisation (Fig. 6.8). The final polymer, when applied to a fibre, should form a structure is shown in fig. 6.9. The surface for maximum repellency. A typical structure is shown in Fig. 6.9. The lenght of the per fluorinated side chains should be about 8-10 carbons. The small spacer group, mostly ethylene, can be modified to improve emulsification and solubility of the polymer.10 co monomers (X, Y, for example stearlyl- or lauryl- methacrylate, butylacrylate, methylol- or epoxy- functional acrylates and block copolymers from x,w-dihydroxydimethylpolysiloxane) affect fabric hand, film.

Plasma Treatment for Preparing Durable Water Repellent

The finishing processes of textiles devoted to improving the quality of the fabric and impart specific properties, such as hydrophobicity, hydrophilicity, anti-

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bacterical, flame retardant, shrink resistance, etc. are becoming always and more important.

Both chemical and physical methods are generally used to obtain specific properties. The conventional treatments, including the widespread dip-coating and padding with chemicals, require the utilization of large amount of chemicals (generally in solution) with important environmental impact. These treatments may also affect the mechanical properties of the fabrics as, for instance, reducing the durability and the comfort to wear.

Alternative techniques have been investigated, during the last years, with the aim of reducing the utilization of chemicals. Among these, plasma treatment attracts particular interest especially for its main peculiarities: the treatments interest only the uppermost layers of the fabric surface without modifying the bulk properties and it is environmental friendly, since the use of chemicals is negligible. The utilization of low pressure plasma processes, in particular, has been widely investigated for the modification of surface properties of textile composed by synthetic polymers and natural materials. The surface modifications and properties depend on the feeding gas and on the operating conditions (input power, pressure, electrode geometry, etc.); a proper selection of these parameters allows to obtain different processes with the same experimental apparatus, i.e. etching, grafting, cross-linking and deposition.

Despite these advantages, there are only few commercial applications of plasma treatments in the textile field, such as the employment of the process to increase the wettability of the fabrics up to 160 cm width developed in a plant build up from Niekmi Institute. In addition to the difficult scale-up from lab to industrial scale, this could be due to the short lifetime of the plasma treatments that very often do not meet the demands of the textile industry in terms of resistance to washing, to light, to perspiration, etc.

Among the different textile properties that can be improved with the plasma technology, the water repellency and the resistance to motor oil stains are very important for automotive applications. Several research groups investigated the hydrophobicity enhancement of polymers and fabrics using plasmas fed with fluorocompounds, e.g. tetrafluoromethane (CF4), sulphur exafluoride (SF6), exafluoroethane (C2F6), exafluoropropene (C3F6), etc. It was found that plasma fed with small molecules (e.g. CF4, C2F6) did not result in treatments of good durability, probably for the formation of short polymer segments dangling on the

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treated surface. For example, a coating with F/C ratio of 1.04 deposited on silk and cotton in plasma fed with C3F6 shows a good hydrophobic character (water contact angle, WCA higher than 120˚), but suffers a partial loss after water- washing and alcohol-extraction.

In this paper, the plasma enhanced-chemical vapor deposition (PE-CVD) with a large fluorinated molecule, the 1H, 1H, 2H-perfluoro-1-decene, is studied in order to impart to the synthetic textile, employed for vehicle interiors in the automotive industry, durable water repellency and anti-stain character respect to motor oil.

It was found that when a 100 nm thick layer with a surface XPS (X-ray photoelectron spectroscopy) F/C ratio higher than 1.4 is deposited, the treated textile is very resistant to water (WCA~150˚) and oil (motor oil contact angle, CA~120˚). These properties are preserved also after usury caused by a test which simulates the wear suffered by a car seat during its use for the average lifetime of the vehicle.

Low Pressure Plasma Treatment Experimental Conditions

Treatments were performed on as received substrates (80 × 80 mm) made of polyethylene terephthalate (PET) and of polyethylene terephthalate thermo-coupled to 5 mm tick polyurethane (PU) foam. These materials are commonly used by the automotive industry for the production of car and commercial vehicles interiors.

The experiments were carried out in the stainless steel, parallel plate, low pressure reactor depicted in Figure 1.

It consists of a cylindrical stainless steel chamber (internal diameter = 200 mm; height: 400 mm) equipped with two stainless steel circular electrodes (diameter = 150 mm, inter-electrode distance = 40 mm), pumped by a turbomolecular-rotary pumping system. The pressure was measured and controlled with a baratron gauge (MKS) and a manual throttle valve, respectively. The upper electrode was connected to a 13.56 MHz radio frequency (RF) power supply though an automatic L-type matching network unit, while, the lower electrode, on which the textile samples were positioned during the deposition processes, was grounded.

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The experiments were performed at 2.0 Pa and 10 - 100 W of input power, with the flow rate of 1H, 1H, 2H- perfluoro-1-decene vapour (Sigma Aldrich, purity > 99.9%) fixed, through a needle valve, at 15 sccm (standard cubic centimeters for minute).

Surface Characterization of Plasma Modified Textiles

The thickness of the coating was determined by means of a KLA Tencor D120 profilometer on Si-c (100) sub-

Figure 1. Schematic of the low pressure plasma reactor strates (flat reference material), partially masked during the deposition process.

The chemical characterization of treated and untreated samples was performed by means of X-ray Photoelectron Spectroscopy, using a Theta Probe spectrometer (Thermo Electron Corporation) equipped with monochromatic Al Kα X-ray source (1486.6 eV), operated at a spot size of 300 µm corresponding to a power of 70 W. Survey (0 - 1200 eV) and high resolution spectra were recorded in FAT (fixed analyzer transmission) mode at a pass energy of 200 and

systemPumping

exhaust

vacuumgauge

RF

matching

vent

textile

monomer

VSC

13

100 eV, respectively. All spectra were acquired at a takeoff angle of 37˚. A flood gun was used to balance surface charging. The C1s signal for the hydrocarbon component (285.0 eV) was used as internal standard for charging correction. Atomic percentages were calculated from the high resolution spectra using the Scofield sensitivity factors set in the XPS data processing software and a non-linear Shirley background subtraction algorithm. Repeated measurements allowed registering a maximum relative standard deviation of about 3%.

Surface morphology of treated and untreated textile was evaluated using a Zeiss SUPRA™ 40 field emission scanning electron microscope (FESEM). Images were acquired after chrome metallization at a tilt angle of 0˚ at an acceleration voltage of 2 KV. The water and oil wettability of textile samples was studied by static and/or dynamic water and motor oil (Red Line synthetic oil, 5w40) contact angle measurements, performed by means of an automatic goniometer (Nordtest), utilizing droplets of 2 µl of volume. The contact angle values were obtained averaging three measurements conducted in different parts of the same sample and on three different samples.

The wear resistance of treated and untreated surfaces was evaluated with a “Cesconi” abrasion tester, according to UNITEX 7858 rule, which reproduces the mechanical stress suffered by a car seat during its normal use for the average lifetime of the vehicle.

The test was carried out employing an abrasimeter general utilized for texting textile, leather, imitation leather (PU; polyvinyl chloride, PVC), non-woven, ceramic, rubber, etc. The abrading unit was made of PET textile fixed on a rotating plate. The substrate to test was located on a rotating “satellite” situated under the rotating plate, as schematized in Figure 2.

The “satellite” and the rotating plate rotated with different speeds, in order to ensure a uniform ablation of the analyzed sample.

A wear cycle of 3000 revolutions was performed with a load of 1 Kg, according to the internal FIAT validation test. Three different samples for each condition were examined.

Ø 50 mm

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Figure 2: Scheme of the wear resistance test device. The substrate to test (D) is mounted on the satellite (F) through a substrate holder (E), while the abrading fabric (C) is fixed on the rotating plate (A) employing the substrate holder (B), on which the weight (P) is applied.

Results and Discussion

The XPS atomic composition and the F/C ratio of the plasma treated uncoupled PET are reported in Table 1, as a function of the input power. The chemical composition of virgin PET is also quoted for comparison.

Under the deposition conditions utilized, the effect of input power on the surface composition of the fluoropolymer coatings is very low. The F/C ratio varies in a narrow range (i.e. 1.47 - 1.65), the highest value is obtained at the lowest input power (20 W), probably for the light plasma fragmentation which preserves the chemical integrity of the monomer. The low effect of input power on the chemical composition of the coatings is reflected also on their hydrophobic/oleophobic behavior. As it can be appreciated in Figure 3, in fact, all samples have similar oil and water contact angles, with a slight reduction by increasing the input power (i.e. decrease of the fluorine content).

Untreated textile, on the other hand, was super-hydrophilic and super-oleophilic, in fact, contact angle measurements were not possible, because the drops of water and oil were instantaneously adsorbed by the sample.

SEM observations showed that all plasma coatings were compact and uniformly covered the fabric.

In order to evaluate the utilization of the optimized plasma treatment to produce water repellent and anti-stain fabric for seat upholstery in automotive field, the

15

experiments were repeated under the same conditions on thermo-coupled PET textile. No difference, respect to the uncoupled substrate, was detected for the water and motor oil contact angle values. This is an important result because it means that the plasma treatment can be performed after the thermo-coupling process between the PET fabric and the polyurethane foam. Since the plasma treatment in part interests also the back side of the fabric, whether the treatment was carried out before the thermo-coupling step, it would result in pour textile-foam adhesion.

The wear resistance of the plasma coated thermo-coupled fabrics was evaluated with the “Cesconi” test described in the section “Materials and Methods”. Figure 4 reports the static contact angles of water and oil, measured after the wear test. All values were collected after 120 seconds of contact of the water/oil drop on the textile surface.

All the samples preserved the hydrophobic character after the test even though, by the comparison with Figure 3, it appears that, except for the sample treated at 100 W, the WCA values decrease after the wear test. Also the static motor oil CA values decrease after the wear test; the lowest reduction is shown by the sample treated at highest input power value (100 W).

Figure 5 clearly shows that the samples with the coatings deposited at 50 and 100 W exhibit a good and stable oleophobic character, also after the wear test. On the contrary, the fabrics coated at 20 and 30 W, despite their initial super-hydrophobic/oleophobic behavior, after the wear test became oleophylic.

The loss of the hydrophobic and oleophobic character suffered by the plasma modified fabrics can be due to mechanical damage caused by the “Cesconi” test. This damage is lower for the coatings deposited at 50 and 100 W, probably for the higher cross-linking promoted by the high input power which results in higher precursor fragmentation and stronger ion bombardment. This is confirmed by the SEM images acquired after the wear test (Figure 6), that clearly show as the coating deposited at 100 W does not suffer serious mechanical damages, while the coating deposited at 20 W is almost completely destroyed after wear test. Also XPS analyses are in agreement with this conclusion, in fact, while the surface chemical composition of the coating deposited at 100

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W shows small changes after the wear test (e.g. the fluorine content decreases from 58% to 51%), the XPS surface

Figure 3. Water and oil contact angle values for plasma coated uncoupled PET textile vs. input power.

Figure 4. WCA and motor oil contact angle values measured after 120 seconds of contact of the worn thermo-coupled textile with the drop. The oil contact angle for the samples treated at 20 W and 30 W was zero.

Table 1. XPS results of uncoupled PET textile, as a function of input power (coating thickness, 100 nm).

Input Power C % O % F % F/C Virgin Textile 74 ± 1 26 ± 2 / /

20 W 37 ± 3 2 ± 1 61 ± 3 1.65 30 W 38.0 ± 0.7 3.1 ± 0.5 58.9 ± 0.6 1.55 50 W 39 ± 2 2.1 ± 0.4 58.9 ± 0.5 1.51 100 W 39.5 ± 0.5 2.5 ± 0.5 58 ± 2 1.47

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chemical composition of the coating deposited at 20 W varies considerably after the wear test (e.g. the fluorine content decreases from 61% to 13.7%).

These experimental evidences allow to conclude that PET textile, thermo coupled with PU foam and coated with 100 nm of a fluorinated thin film deposited in low pressure plasma at 100 W, can be considered as possible, durable, water repellent and anti-stain material for automotive uses.

In this paper, a durable water/motor oil resistant fluorinated coating (F/C ≥ 1.47) was deposited in low pressure plasma conditions. The optimized film was used to cover the thermo coupled with 5 mm of polyurethane foam synthetic textile, generally used in automotive field. The obtained fabrics were wear resistant, particularly if they

Figure 5. Dynamic motor oil contact angle values after “Cesconi” test for plasma coated thermo-coupled textile.

(a)

120

80

100

60

40

20

0

virgin

W20pd W30pd

W50pd

W100pd

12010080604020).sec(time

)°(CAoil

time (sec.)

oil CA

120100806040200

120

100

80

60

40

20

0

18

(b)

Figure 6. SEM images (magnification 1 and 5 Kx) of PET textile, thermo coupled with 5 mm of PU foam, coated with plasma coatings after “Cesconi”

were modified at high value of input power.

The optimized deposition process can be potentially employed in automotive field to obtain durable, water repellent and anti-stain textiles useful for the realization of car and commercial vehicle interiors.

Paraffin Wax Emulsion as Water Repellent

Paraffin wax emulsion is prepared by emulsifying paraffin wax (PW) in water using stearic acid (SA) and triethanolamine (TEA) emulsifying system. A mother emulsion is prepared at different concentrations of PW (10.5—19.1%w/w) and SA (4.5—13%w/w) neutralized to different extents by TEA (25—100% degree of neutralization). Upon treating 50/50 cotton/polyester fabric with a padding solution containing 50 g/L of different mother emulsions, its water repellency does not exceed the value of 50. Aluminum chloride proves to be the best deactivating agent of the hydrophilicity of the emulsifying agent among other salts including barium chloride, zinc sulfate, and aluminum sulfate. Optimum emulsion ingredients are found to be PW (10.5%w/w), SA (4.5% w/w), TEA (2.4% w/w, to attain full neutralization of SA), and SA/AlCl3 molar ratio (1/1). Treating the fabric with the deactivated emulsion results in enhancing its water repellency rating (up to 80), decreasing its surface roughness, and increasing its stiffness. A scanning electron micrograph of the treated fabric shows the deposition of the emulsified wax on the fabric surface. Treating the fabric with the emulsion in the presence of a fluorochemical finish, namely Nuva FB of Clariant, proves that the

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first can be used as an extender for the second. Raising the drying temperature to 160·C gives rise to a water-repellency rating of 100.

Metal Soaps for the Production of Integral Water Repellent Concrete Water absorption into and water migration in concrete is at the origin of major degradation mechanisms of reinforced concrete structures. The structure of concrete can be weakened by hydrolysis [1, 2], high water content increases the risk of frost damage, and aggressive compounds dissolved in water can be transported deep into the pore space of concrete by capillary action [3, 4]. Capillary absorption of concrete can be practically suppressed by water repellent treatment of the surface. In this way durability and service life of reinforced concrete structures can be significantly increased. Thousands of years ago natural products such as oils, fats or waxes have been applied to avoid excessive water uptake by capillary action of natural stones and cement-based materials. More recently silane-based compounds are used in practice. In most cases the surface of hardened concrete is impregnated with liquid silane [3]. Silane reacts in the pore space of concrete and forms finally a thin network of silicon resin on the surface of hydration products of cement. Bridges tunnels and other important elements of the infrastructure have been and are protected successfully by water repellent surface treatment for many years by now. In some cases it would be more convenient if the entire volume of concrete would be water repellent. This aim cannot be achieved, however, by surface impregnation of structural elements with conventional dimensions, as the penetration depth is seldom more than 10 mm. Structural concrete elements can be made integral water repellent, however, by adding silane emulsion to the fresh mix for instance [4]. Recent test series have shown that deep surface impregnation is more efficient than integral water repellent treatment. But

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service life of reinforced concrete structures can still be significantly increased by integral water repellent concrete. In this contribution the efficiency of metal soaps for the production of integral water repellent concrete shall be investigated. Although metal soaps are used in practice for many years already in different cementbased products very few publications on capillary absorption of concrete with metal soaps added exist in the literature [5-7]. One major aim of this contribution is to find out if addition of metal soaps to fresh concrete is a promising technology to increase service life of reinforced concrete structures in aggressive environment.

Experimental

For all tests described in this contribution a standard concrete with a watercement ratio of 0.5 has been prepared as a basis for reference. The composition of this concrete is given in Table 1. Ordinary Portland cement, river sand with a maximum diameter of 5 mm and broken coarse aggregate with a maximum diameter of 25 mm, both from Qingdao region, have been used.

Table 1: Composition of plain concrete given as kg/m3

Components

Cement Gravel Sand Water W/C

Mass/volume

320 1267 653 160 0.5

0.5 % and 1 %, related to the mass of cement, of four types of metal soaps have been added to all four different types of concrete. The metal soaps have been obtained from Peter Greven Fett-Chemie Company, Germany. The four types of metal soaps have the following designation: LIGAPHOB ZN 502, LIGA Zinkstearat 101, LIGA Calciumstearat 860, and LIGAPHOB ZN 101 PLUS.

First cubes with an edge length of 100 mm have been cast in steel forms. After one day curing under wet burlap, the steel form has been removed and the cubes were allowed to harden in a humid chamber (T=20 °C, RH>95 %). At an age of 28 days the cubes were cut into two halves parallel to the direction of casting. These half cubes were then exposed to the laboratory atmosphere (T=20 °C and RH=65 %)for four weeks for drying. Then the four small surfaces

21

(50 x 100 mm) were sealed with wax. The specimens were then ready for capillary absorption. The surface originally in contact with the steel form of each half cube was then put in contact with water or with 5 % aqueous NaCl solution. The weight gain has been measured by weighing after regular intervals of absorption.

Results and discussion

Compressive strength

Compressive strength of the different types of concrete has been determined at an age of 28 days in order to characterize mechanical properties. Results are compiled in Table 2. Each value given in Table 2 is the average of at least 3 test results. Addition of metal soap to the fresh concrete reduces compressive strength significantly. The compressive strength may be reduced by up to 50 % of the strength of neat reference concrete by addition of 1 % of metal soap. This observation is an indication that the presence of metal soaps in the pore liquid has a strong influence on hydration of Portland cement. For practical applications this strength decrease has to be compensated by a reduction of the watercement ratio.

Table 2: Compressive strength of neat concrete (reference) and concrete with different metal soaps added

Dosage %

Compressive strength MPa %

Neat concrete 0 54.2 100

LIGAPHOB ZN 502 0.5 35.0 64.6 1.0 30.4 56.1

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Zinkstearat 101 0.5 37.2 68.6 1.0 29.8 55.0

LIGA Calciumstearat 860

0.5 34.6 63.8 1.0 31.0 57.2

LIGAPHOB ZN101 Plus

0.5 32.7 60.3 1.0 27.0 49.8

Capillary absorption

The absorption of water by capillary action has been measured as function of time. Results have been plotted on a square root of time scale and they are shown in Figure 1.

Metal soaps

Figure 1: Capillary water absorption by neat concrete and by integral water repellent concrete with metal soaps

Table 3: Initial coefficient of capillary absorption Ai for neat concrete and concrete containing metal soaps

Dosage %

Coefficient Ai

g/m2 h0.5 Coefficient Ai

% Neat concrete 0 312 100 LIGAPHOB ZN 502 0.5 195 62.5

abso

rbed

w

ater

,g/m

2

23

1.0 76 24.4

Zinkstearat 101

0.5 79 25.3 1.0 82 26.6

LIGA Calciumstearat

860

0.5 91 29.2 1.0 93 29.8

LIGAPHOB ZN101

Plus

0.5 52 16.7 1.5 74 23.7

In a simple capillary porous system the water uptake as function of time can be described approximately by means of a square root of time function:

(1) ∆W t( )= A t

This function describes capillary absorption of concrete within certain time intervals only in a realistic way. Because of several influences the coefficient of capillary absorption A depends on the penetration depth. One major reason is the fact that the skin of concrete has a higher porosity than the bulk material. But we can use the initial value of Ai to characterize capillary absorption of concrete and the influence of added metal soaps on capillary absorption. Values determined for the first hour of contact between the concrete surface and water are compiled in Table 3.

Capillary absorption is significantly reduced by addition of metal soaps. It can be observed, however, that addition of 1 % of a metal soap does not reduce further capillary absorption as compared with concrete containing 0.5 %, with the exception of LIGAPHOB ZN 502. With the three other metal soaps a slight increase of capillary absorption is observed even when dosage is increased from 0.5 % to 1 %. Further studies are needed to find out an optimum dosage of metal soaps. It may well be below 0.5 %.

On concrete, which has been made integral water repellent by addition of silane emulsion it has been observed that the siloxane concentration was at maximum close to the surface [8]. It may be assumed that silane emulsion is transported during the drying process with the water into the surface near zone, where it can react. In order to check if in concrete made integral water repellent with metal

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soaps a similar effect can be observed a layer with a thickness of 5 mm has been cut of the surface with a diamond saw. Then capillary absorption through the fresh surface has been determined again. Results of this second series of tests are shown in Figure 2.

Figure 2: Capillary water absorption by neat concrete and by integral water repellent concrete with metal soaps after removal of a 5 mm thick surface layer Comparing results shown in figures 1 and 2 it is obvious that capillary suction increases considerably after removing the surface near zone. This is a clear indication that also in this case the surface near zone is more water repellent than the bulk material. This observation has been confirmed by direct determination of the content of stearates as function of the distance from the surface. As the untreated specimens also absorb less water per unit of time traces of oil from the steel form have probably also contributed to a reduction of capillary absorption. The initial coefficient of capillary absorption Ai has been determined and is shown in Table 4. While the coefficient of capillary absorption Ai as measured directly on the formed surface is reduced to values between 16 and 30 % of the reference concrete, the coefficient as measured after removal of a 5 mm thick surface layer is reduced to values between 41 and 62 %. Capillary absorption has also been determined after removal of two additional layers with a thickness of 10 and 40 mm. No significant further reduction of the efficiency of metal soaps could be observed.

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Table 4: Initial coefficient of capillary absorption Ai for neat concrete and concrete containing metal soaps after removal of a 5 mm thick surface layer

Dosage

%

Coefficient Ai

g/m2 h0.5 Coefficient Ai

% Neat concrete 0 358 100 LIGAPHOB ZN 502

0.5 189 52.8 1.0 171 47.8

Zinkstearat 101

0.5 192 53.6 1.0 179 50.0

LIGA Calciumstearat

860

0.5 212 59.2 1.0 222 62.0

LIGAPHOB ZN101

Plus

0.5 189 52.8 1.5 148 41.3

Chloride penetration

Water penetration by capillary action is of course an indication of the risk of penetration of chloride or any other aggressive compound dissolved in water into the pore space. The rate of chloride penetration is a dominant parameter for the estimation of service life of reinforced concrete structures in marine environment or in frequent contact with de-icing salt. After 28 days of contact with a 5 % aqueous NaCl solution the chloride profile as established in the concrete specimens has been determined.

From the surface of the chloride contaminated specimens thin layers have been milled successively. The chloride content of the powder, which has been collected, has been determined by means of ion chromatography. Chloride profiles obtained in this way are shown in Figure 3.

It can be seen that after 28 days of contact of the concrete surface with the salt solution chloride has penetrated deeper than 20 mm into the neat concrete specimens. There is a wide scatter of the obtained chloride profiles of concrete

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containing metal soaps and more experiments will be necessary to obtain more reliable and quantitative results. Results obtained on specimens containing 0.5 % LIGAPHOB ZN 502 are doubtful and must be repeated, but the chloride profile of all other specimens containing metal soap are shifted to lower penetration depth. This shift is a direct measure for the extension of service life of reinforced concrete structures in aggressive environment by adding metal soaps to the fresh concrete. Addition of 1 % of LIGAPHOB ZN 502 and of 1 % of LIGAPHOB ZN 101 Plus leads practically to an effective Chloride barrier. By optimising the concrete composition the resistance with respect to chloride penetration can certainly be further improved.

Figure 3: Chloride profiles as observed in neat concrete and concrete exposed to 5 % aqueous NaCl solution for 28 days

It has been shown that it is possible to produce integral water repellent concrete by addition of metal soaps to fresh concrete. By adding 1 % of LIGAPHOB ZN 502 or 1 % of LIGAPHOB ZN 101 Plus chloride penetration is reduced to such an extent that the integral water repellent concrete can be considered to be equipped with an effective chloride barrier. Surface life of reinforced concrete structures in aggressive environment built with this type of concrete will be extended significantly.

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After optimization this type of concrete will be a substantial contribution to more durable and more sustainable construction.

Strain-hardening cement-based composites (SHCC) [9] and textile cement composites [10] are comparatively new and advanced building materials. High ductility is reached in both cases by controlled multi-cack formation. It is recommended to add metal soaps to the fresh mix of these two types of materials in order to avoid capillary absorption by micro-cracks [. This will improve durability and extend service life in aggressive environment significantly.