TAB 9--Dow 888 Sealant info..pdf

Product Information

Silicone Sealants

FEATURES

• Easy to use

• All-temperature gunnability

• Unprimed adhesion

• Seals irregular surfaces

• High movement capability

• Low modulus

• Fully elastic

• Resilient

• Good weatherability

• Fast cure – typically tack-free surface in one hour or less

• Long-life reliability

COMPOSITION

• One-part, cold-applied silicone that cures to a durable, flexible, low-modulus silicone rubber joint seal

Dow Corning® 888 Silicone Joint Sealant

Low-modulus silicone sealant for new and remedial joint sealing applications in Portland cement concrete

APPLICATIONS

• Sealing transverse contraction and expansion joints, longitudinal, center line and shoulder joints in Portland cement concrete (PCC)

TYPICAL PROPERTIES

Specification Writers: Please contact your local Dow Corning Sales Application Engineer or Dow Corning Customer Service before writing specifications on this product.

Test Unit Result

As Supplied Color Gray Flow, Sag or Slump Nil Extrusion Rate grams per minute 90-250 Specific Gravity 1.450-1.515 Skin-Over Time, at 25°C (77°F) minutes 10 Tack-Free Time, at 25°C (77°F) minutes 60 Cure Time, at 25°C (77°F) days 7-14 Full Adhesion days 14-21

As Cured – after 7 days at 25°C (77°F) and 50 percent RH Elongation, minimum percent 1200 Modulus, at 150 percent elongation, maximum psi (kPa) 45 (310) Durometer Hardness, Shore A points 15-25 Joint Movement Capability, +100/-50 percent, 10 cycles No failure Adhesion to Concrete, minimum elongation percent +500

DESCRIPTION

Dow Corning® 888 Silicone Joint Sealant can be used as the original sealant in new concrete construction or as a remedial or repair sealant in old construction. In new construction, it provides the extra insurance needed if all the “shrink” or contraction cracks do not occur during the initial “weak-ening” step. Thus, two or three con-crete lengths act in unison, stressing a sealant two or three times the design dimensions or movement.

Because of its low-modulus character-istics and good extension/compression recovery (+100/-50 percent of original joint width), Dow Corning 888 Silicone

Joint Sealant gives outstanding performance in highway, airport and bridge joints in which high movement occurs.

Highway concrete contraction/ expansion joints are generally sealed to prevent erosion of pavement sub-base and/or corrosion of metal tie bars embedded in the concrete. Such cor-rosion results from water and deicing chemicals entering the joints at the pavement surface.

Sealing of highway joints also pre-vents spalling and breakage of con-crete along the slab edge, which occurs when noncompressibles (dirt, stones and/or ice) are forced into or form in the joint.

For use in repair or remedial applications where other joint sealing materials have failed because of excessive movement or poor weather-ability, Dow Corning 888 Silicone Joint Sealant can be used to seal irregularly shaped and/or spalled joints. Thus, the joints do not need reforming before sealing. These joints should be dry and free of all old sealing compounds.

Benefits

• Easy to use – one-component, cold-applied, ready-to-use as supplied;

no mixing required; dispensed directly from bulk container into joint by hand or with an air-powered pump.

• All-temperature gunnability – consistency is relatively unchanged over normal installation temperature range.

• Unprimed adhesion – primer is not required for bonding to PCC. For optimum adhesion, the surface must be clean, dry and frost-free.

• Seals irregular surfaces – can be used to seal joints where spalls have occurred, provided adequate contact is made between sealant and substrate.

• High movement capability – the sealant will perform in a continuous joint movement of +100/-50 percent. In new construction, it will take the 25 percent movement of each of two or three slab lengths working in unison before all the “shrink” or contraction cracks occur.

• Low modulus – the sealant stretches 100 percent in the joint with very little force. This places very little strain on the bond line or joint wall, which maximizes the probability of a successful seal with continuous joint movement. Joint movement caused by temperature, traffic and faulting requires a sealant that does not strongly resist stress and/or shear.

• Fully elastic – the sealant can be stretched to 100 percent or com-pressed to 50 percent of the joint bond width and held there. When released, it will recover 95 percent or greater of the original dimension. The extension and/or compression can be repeated many times and the sealant will resume its original shape without splits or cracks. Thus, when properly installed in a highway contraction joint, it does not “pump” out of the joint during compression. Nor does it split, crack or lose adhesion during extension.

• Resilient – once cured, the sealant prevents stones and other noncom-pressibles from entering the joint by “squeezing” them out as soon as the force pushing these noncompres-sibles into the sealant is removed.

• Good weatherability – its 100 per-cent silicone rubber is virtually unaffected by sunlight, rain, snow, ozone or temperature extremes.

• Fast cure – typically, the sealant will have a tack-free surface in one hour or less. With this fast cure and recessed joint design, the road can be opened soon after sealing in most applications.

• Long-life reliability – under normal conditions, cured sealant stays rubbery from -45 to 149°C (-49 to 300°F) without tearing, cracking or becoming brittle.

Applicable Standards Meets and/or exceeds ASTM D 5893- 96 “Standard Specification for Cold Applied, Single Component, Chemically Curing Silicone Joint Sealant for Portland Cement Concrete Pavements,” Type NS (Non-Sag). In addition, the Federal Aviation Administration has published the “FAA Engineering Brief 36 – Silicone Joint Sealants.” This publication approves the use of these materials in airfield situations.

Meets and exceeds both Federal Specifications TT-S-001543A Class A (one-part silicone sealants) and TT-S- 00230C Class A (one-component sealants) that were written for construction sealants requiring extremely high movement capability.

Also meets Canadian Specification 19GP9 Type I and approximately 41 Department of Transportation (DOT)

Figure 1: Good Joint Design

1. Joint width wide enough to accommodate movement. (For additional information on joint width, see papers by Spells and Klosowski, “Silicone Sealants for Use in Concrete Construction,” Vol. 1, No. 1, American Concrete Institute, SP-70, 1981; J.B. Cook, “Construction Sealants and Adhesives,” Wiley-Interscience, 1970; and J.M. Klosowski, “Sealants in Construction,” Marcel Dekker, 1989.)

2. Joint sawed deep enough to allow backer rod/sealant placement and space for pumping of old sealant compounds. NOTE: This applies to standard joints only; void space beneath backer rod in new construction is not needed.

3. Proper backer rod placement to prevent three-sided adhesion.

4. Sealant installed to proper depth and width.

5. Sealant tooled 1/4 to 1/2 inch (6 to 13 mm) below pavement surface.

6. Depth of lowest slab determines the amount of recess required if grinding is anticipated;

once grinding is complete, the sealant will have proper recess below the pavement surface.

SHALLOW CUT JOINT FOR

NEW CONSTRUCTION

DESIGN IF GRINDING IS

ANTICIPATED

STANDARD JOINT

specifications that require a low-modulus sealant with high movement capability.

HOW TO USE

Please refer to the Pocket Installation Guide for additional information on applications, preparation and installa-tion information.

Low-modulus Dow Corning 888 Silicone Joint Sealant easily with-stands extreme joint movement when properly applied. The sealant will withstand 100 percent extension and 50 percent compression of the original joint width. However, the recom-mended joint movement design is for ±25 percent (50 percent total) and not at the sealant limits. This difference ensures a successful seal when job site joint widths are different than designed widths. Therefore, the joint design dimensions should be less than the ultimate sealant capability.

A thin bead of silicone sealant will accommodate more movement than a thick bead. Dow Corning 888 Silicone Joint Sealant should be no thicker than 1/2 inch (13 mm) and no thinner than 1/4 inch (6 mm). Within these limits, the sealant width-to-depth ratio should be 2:1.

In all cases, the sealant must be recessed below the pavement surface at least 3/8 inch (9 mm) with 1/2 inch (13 mm) recess being acceptable in wider joints (see Table I). Consider-ation should also be given to other possible road-working operations, such as diamond-grinding of the surface. Activities of this type would require the sealant bead to be recessed even deeper.

Dow Corning 888 Silicone Joint Sealant is a nonsag sealant. This allows its use in vertical curb joints as well as horizontal joints.

Being a non-leveling sealant, Dow Corning 888 Silicone Joint Sealant must be “tooled” to ensure good contact and adhesion as well as to control sealant depth and provide a recessed surface. Several devices can be used for tooling. Among the simplest and easiest to obtain is the expanded closed-cell polyethylene foam backer rod, which must be larger than the joint width.

In new construction where the joint is a new cut, a shallow cut is recom-mended where the backer rod is placed on the “shelf ” or bottom of the joint (see Figure 1). Recommended depths are shown in Table I. This design provides a firm support for sealant tooling, making the sealant easier to install, and further ensures good sealant/concrete contact. A shallow cut design also saves saw blades and time.

Table I: Recommended Backer Rod Installation (Shallow Cut)1

Measured in Inches

Joint Width 1/4" 3/8" 1/2" 3/4" 1" 2"

Recessed Below Surface 3/8" 3/8" 3/8" 3/8" 3/8-1/2" 3/8-1/2" Sealant Thickness 1/4" 1/4" 1/4" 3/8" 1/2" 1/2" Backer Rod Diameter 3/8" 1/2" 5/8" 7/8" 11/4" 21/2"

Total Joint Depth 1-11/8" 11/8-11/4" 11/4-13/8" 15/8-13/4" 21/4-23/8" 21/2-25/8"

Measured in Millimeters

Joint Width 6 mm 9 mm 13 mm 19 mm 25 mm 51 mm

Recessed Below Surface 9 mm 9 mm 9 mm 9 mm 9-13 mm 9-13 mm Sealant Thickness 6 mm 6 mm 6 mm 9 mm 13 mm 13 mm Backer Rod Diameter 9 mm 13 mm 16 mm 22 mm 32 mm 64 mm

Total Joint Depth 25-29 mm 29-32 mm 32-35 mm 41-44 mm 57-60 mm 64-67 mm

1On road surfaces where grinding is planned at a later date, the sealant and backer rod should be installed so that sealant is approximately 3/8 inch (9 mm) below the road surface after grinding is complete. An additional small amount should be added to allow for surface imperfections on the bottom and to provide room for old sealant to pump up from below during rehabilitation work in the summer months.

In repair work where previous sealing materials have been of a joint filling type rather than a joint sealing type, or where the joint is not broadened by sawing, a standard joint design is recommended in which the backer rod is slightly above the shelf. Extra space (1/4 to 1/2 inch [6 to 13 mm]) between the bottom of the backer rod and shelf should be provided to allow for possible “pumping” of old joint filling material from the bottom of the joint.

It is recommended that care be given to selection of proper oversized backer, so that a firm tooling support is obtained (generally 1/4 inch [6 mm] larger than the joint works quite well).

Dow Corning 888 Silicone Joint Sealant is part of a system that must include the proper backer rod and proper installation procedures. The backer rod must be expanded closed-cell polyethylene foam. Where irreg-ularly shaped joints exist, backer rod that is open-cell with an impervious skin is recommended to ensure a tight fit. Several other back-up materials (paper, fibrous ropes and open cell foam) are available, but have proven to be unacceptable. There are several manufacturers of closed-cell poly-ethylene foam and any may be used.

Please refer to the Pocket Installation Guide for more information on appli-cations, preparation and installation information.

Printed in USA Dow Corning is a registered trademark of Dow Corning Corporation.

Form No. 61-408L-01 AGP7387 ©1997-2005 Dow Corning Corporation. All rights reserved.

HANDLING PRECAUTIONS

PRODUCT SAFETY INFORMATION

REQUIRED FOR SAFE USE IS NOT

INCLUDED IN THIS DOCUMENT.

BEFORE HANDLING, READ PROD-

UCT AND MATERIAL SAFETY

DATA SHEETS AND CONTAINER

LABELS FOR SAFE USE, PHYSICAL

AND HEALTH HAZARD INFORMA-

TION. THE MATERIAL SAFETY

DATA SHEET IS AVAILABLE ON THE

DOW CORNING WEBSITE AT

WWW.DOWCORNING.COM, OR

FROM YOUR DOW CORNING SALES

APPLICATION ENGINEER, OR

DISTRIBUTOR, OR BY CALLING

DOW CORNING CUSTOMER

SERVICE.

USABLE LIFE AND

STORAGE

When stored in original, unopened containers between 0°C (32°F) and 32°C (90°F), Dow Corning 888 Silicone Joint Sealant has a shelf life of 12 months from date of manufac-ture. Keep containers tightly closed.

Refer to product packaging for “Use By Date.”

PACKAGING

Dow Corning 888 Silicone Joint Sealant is supplied in 29-fl oz (857-mL) disposable cartridges, 4.5-gal (17-L) bulk pails, and 50-gal (189-L) bulk drums.

LIMITATIONS

Dow Corning 888 Silicone Joint Sealant is not recommended for conditions where continuous water/ moisture exposure is expected. It should not be applied in totally confined spaces where the sealant is not exposed to atmospheric moisture.

The sealant should never be applied to wet or damp concrete or installed during inclement weather. New concrete should be allowed to cure and dry for at least 7 days of good drying weather. For each day of rain that occurs during that period, an additional day should be added to the 7-day drying time. For “Fastrack” or high early concrete mixes, please contact your Dow Corning Technical Service Representative.

The sealant bead should be recessed below the pavement surface to prevent abrasion from traffic and snow removal equipment.

The adhesion to substrates other than PCC should be checked before performing full-scale sealing. Contact your Dow Corning Technical Service Representative.

Dow Corning does not promote or warrant the use of Dow Corning® brand sealants in applications associated with spill containment areas of any kind.

This product is neither tested nor represented as suitable for medical or pharmaceutical uses.

HEALTH AND

ENVIRONMENTAL

INFORMATION

To support customers in their product safety needs, Dow Corning has an extensive Product Stewardship organ-ization and a team of Product Safety and Regulatory Compliance (PS&RC) specialists available in each area.

For further information, please see our website, www.dowcorning.com, or consult your local Dow Corning Sales Application Engineer.

LIMITED WARRANTY

INFORMATION – PLEASE

READ CAREFULLY

The information contained herein is offered in good faith and is believed to be accurate. However, because con-ditions and methods of use of our products are beyond our control, this information should not be used in substitution for customer’s tests to ensure that Dow Corning’s products are safe, effective, and fully satisfactory for the intended end use. Suggestions of use shall not be taken as induce-ments to infringe any patent.

Dow Corning’s sole warranty is that the product will meet the Dow Corning sales specifications in effect at the time of shipment.

Your exclusive remedy for breach of such warranty is limited to refund of purchase price or replacement of any product shown to be other than as warranted.

DOW CORNING SPECIFICALLY

DISCLAIMS ANY OTHER

EXPRESS OR IMPLIED

WARRANTY OF FITNESS FOR A

PARTICULAR PURPOSE OR

MERCHANTABILITY.

DOW CORNING DISCLAIMS

LIABILITY FOR ANY INCIDEN-

TAL OR CONSEQUENTIAL

DAMAGES.

Your local distributor is:

For more information on these products, please refer to Dow Corning’s technical data sheets and installa-tion guides, or call Dow Corning Customer Service at

(989) 496-6000 or 1-800-322-8723.

Visit our website at www.dowcorning.com.

I N S T A L L A T I O N G U I D E

Dow Corning® brand Silicone Pavement

Sealants

A V

WE HELP YOU INVENT

THE FUTURE.™

www.dowcorning.com

LIMITED WARRANTY INFORMATION – PLEASE READ CAREFULLY

The information contained herein is offered in good faith and is believed to be accurate. How-ever, because conditions and methods of use of our products are beyond our control, this infor-mation should not be used in substitution for customer’s tests to ensure that Dow Corning’s prod-ucts are safe, effective, and fully satisfactory for the intended end use. Suggestions of use shall not be taken as inducements to infringe any patent.

Dow Corning’s sole warranty is that the product will meet the Dow Corning sales specifications in effect at the time of shipment. Your exclusive remedy for breach of such warranty is limited to refund of purchase price or replacement of any product shown to be other than as warranted.

DOW CORNING SPECIFICALLY DISCLAIMS ANY OTHER EXPRESS OR IMPLIED

WARRANTY OF FITNESS FOR A PARTICULAR PURPOSE OR MERCHANTABILITY.

DOW CORNING DISCLAIMS LIABILITY FOR ANY INCIDENTAL OR CONSEQUENTIAL

DAMAGES.

Dow Corning is a registered trademark of Dow Corning Corporation.

WE HELP YOU INVENT THE FUTURE is a trademark of Dow Corning Corporation.

©1996, 2000, 2002 Dow Corning Corporation. All rights reserved.

Printed in USA AGP6278 Form No. 61-507N-01

S I L I C O N E P A V E M E N T S E A L A N T S

Contents

Preface

Dow Corning brand Silicone Pavement Sealants

What are they?

Where to Use Them

Other Applications

Important Considerations

Figure 1 – Standard Field Adhesion Hand Pull Test

How to Use Dow Corning Silicone Pavement Sealants

Cure Characteristics

Joint Design

Joint Width

Figure 2 – Joint Design Considerations:

Dow Corning ® 888 Silicone Joint Sealant

Figure 3 – Joint Design Considerations:

Dow Corning ® 890-SL Self-Leveling Silicone Joint Sealant

Joint Depth

Joint Preparation

Backer Rod Selection

Sealant and Backer Rod Placement Depths

Sealing New Concrete Pavement

Resealing Old Concrete Pavement

Table 1 – Theoretical Estimating Requirements

Table 2 – Metric Estimating Equivalents

Full Depth Asphalt Pavements

Sealing New Asphalt Pavements

Resealing Old Asphalt Pavements

Asphalt Overlays

Sealing Joints in New Asphalt Overlays

Sealing Reflection Cracks in Older Asphalt Overlays

A V

Sealing Concrete/Asphalt Shoulder Joints

Backer Material Installation

Figure 4 – Backer Rod Installation Tools

Sealant Installation

Installation Equipment

Figure 5 – Extrusion Pump

Table 3 – Manufacturers of Power Installation Equipment

Table 4 – Pump Manufacturers’ Recommendations

Table 5 – Manufacturers of Manual Installation Equipment

Sample Specification for Dow Corning 888 Silicone Joint Sealant

Sample Specification for Dow Corning 890-SL Self-Leveling Silicone Joint Sealant

Questions and Answers

Key Word Index

Preface

Highway and airport joints call for a tough sealant that can withstand excessive horizontal and vertical movement, has good weatherability and is easy to install with a short downtime and long service life.

Dow Corning ® brand silicone pavement sealants can do the job. Dow Corning ® 888 Silicone Joint Sealant and Dow Corning ®

890-SL Self-Leveling Silicone Joint Sealant are one-part silicone formulations that can be installed in new or old joints in Portland Cement Concrete (PCC) pavement over a wide temperature range.

In addition, Dow Corning 890-SL Self-Leveling Silicone Joint Sealant can be used on asphalt. These sealants cure upon exposure to moisture in the air to form a permanently flexible, low- to ultra-low-modulus, high-elongation silicone rubber seal. These sealants will collectively be referred to as Dow Corning silicone pavement sealants throughout this guide.

Dow Corning silicone pavement sealants are capable of with-standing extension of 100 percent and compression of 50 percent of the original joint width. They have excellent recovery, which makes them ideal for use in joints that experience a high degree of movement. Dow Corning 890-SL Self-Leveling Silicone Joint Sealant is an ultra-low modulus sealant that can be used to seal joints in asphalt pavements because it places very little stress on the asphalt surface. Asphalt paving materials have low tensile strengths and require a sealant that places very little stress on the asphalt itself while keeping the joint sealed.

To fully utilize these capabilities, the sealant must be properly installed in properly designed joints. This pamphlet provides the correct installation procedures, which begin with good joint design and preparation. A sample specification is provided for these products. The pamphlet also covers backer rod installation, giving a list of installation equipment and manufacturers of recommended equipment, as well as the most frequently asked questions and answers.

Dow Corning Silicone Pavement Sealants

What are they?

Dow Corning silicone pavement sealants are members of the same family and are based upon similar technologies.

Dow Corning 888 Silicone Joint Sealant is a one-part, non-self-leveling silicone formulation that can be installed over a wide temperature range. It requires tooling and cures on exposure to atmospheric moisture to form a durable, flexible, low-modulus, high-elongation, silicone rubber joint sealant for use on Portland Cement Concrete. Primer is not required on most applications.

During application, no heating or cooling of the sealant is required, as the material consistency remains relatively unchanged (as compared with nonsilicone-based materials) from -35 to 140°F (-32 to 60°C). It retains its gunnability and can be pumped at low temperatures.

Dow Corning 890-SL Self-Leveling Silicone Joint Sealant is a one-part, self-leveling silicone sealant that readily extrudes over a wide temperature range. It cures on exposure to atmospheric moisture to form a durable, flexible, ultra-low-modulus, high-elongation silicone rubber joint seal for use on asphalt and/or Portland Cement Concrete. Primer is not required on most applications. During application, no heating or cooling of the sealant is required, as the material consistency remains relatively unchanged (as compared with nonsilicone-based materials) from -35 to 140°F (-32 to 60°C). It retains its gunnability and can be pumped at low temperatures.

Where to Use Them Dow Corning 888 Silicone Joint Sealant is ideal for use in concrete-to-concrete joints (PCC) that experience a high degree of movement, such as transverse pavement expansion and contraction joints in highways, airports and pavements. It withstands extension of 100 percent and compression of 50 percent of original joint width and has excellent recovery. It can be used in transverse, longitudinal, centerline and shoulder joints. Its non-slump characteristic makes it an excellent choice for vertical joints in curbs. It is often used in remedial work, especially where other materials have failed because of excessive movement or poor weatherability.

Dow Corning 890-SL Self-Leveling Silicone Joint Sealant is ideal for use in asphalt-to-concrete, concrete-to-concrete or asphalt-to-asphalt joints that experience a high degree of move-ment, such as transverse pavement expansion and contraction joints in highways, airports and pavements. It can be used in longitudinal, centerline and shoulder joints. It is also ideal for use in sealing asphalt-to-asphalt joints in new asphalt overlays or joints prepared over reflection cracks in old asphalt overlays. Its self-leveling characteristic makes it an excellent choice for hor-izontal joints and for joints on moderate slopes. It can also be used in remedial work where other materials have failed because of excessive movement or poor weatherability.

Dow Corning silicone pavement sealants are not recommended for use in totally confined joints where the sealant is not exposed to atmospheric moisture during cure. Additionally, these sealants are not recommended for use in applications involving continuous or semicontinuous water immersion.

Dow Corning 888 Silicone Joint Sealant should be tooled with a recess below the pavement surface to minimize abrasion from traffic and snow removal equipment. Dow Corning 890-SL Self- Leveling Silicone Joint Sealant requires no tooling. Experience has shown that better silicone pavement joint performance can be obtained by maintaining a recess of 3/8 inch (9.53 mm) or greater.

Other Applications Contact your Dow Corning representative for more information on the applications listed below or others:

• Airport Runways • Fast Track Pavements

• Loop Seals • Random Crack Sealing

• Pavements on Grades • Bridge Joints

• Steel/Armor Joints • Jet Fuel Resistance

Important Considerations

JOINT FACES MUST BE CLEAN, DRY, AND FROST-FREE

WHEN THE SEALANT IS INSTALLED. JOINTS MUST BE

FREE OF STANDING WATER, AND UNDER NO CIRCUM-

STANCES SHALL SEALING TAKE PLACE DURING

INCLEMENT WEATHER.

Joint Cleanliness – A clean joint shall have no visible signs of residual sealant or debris on the joint face, and will leave no residual cement powder or dust on your fingers after rubbing the joint face.

Pavement Drainage – Dow Corning silicone pavement sealants are not recommended for conditions where continuous water/ moisture exposure is expected. Sources of subsurface water infiltration include a high water table, shallow or poor drainage ditches, or improperly designed or maintained subsurface drainage systems. All potential applications should be reviewed to ensure that the pavement has positive drainage. The correct application of a primer has been shown to enhance performance of the sealant in these situations; contact your Dow Corning representative for more details.

Dew Point – The temperature at which the air is saturated with moisture vapor and liquid water (dew) begins to form. Do not install sealant when the temperature is below the dew point.

Inclement Weather – If rain or other inclement weather occurs during joint preparation or sealing, all operations should cease and sufficient time must be allowed so that the joints are dry prior to starting/continuing the sealing operation.

IN NO CASE SHOULD SEALANT BE INSTALLED IN A

JOINT THAT HAS STANDING WATER.

Prior to work of any kind pertaining to joint sealing, the joint sealing contractor, in conjuction with the owner or owner’s representative and Dow Corning, must meet and discuss method of installation and install a test section. A field adhesion test must be performed on the test section as outlined in Dow Corning’s field adhesion test procedure to confirm adhesion under site conditions.

Figure 1 – Standard Field Adhesion Hand Pull Test

The field adhesion test is a simple screening procedure that may help detect application problems such as improper cleaning, use of improper primer, poor primer application or improper joint configuration.

1. Make a knife cut horizontally from one side of the joint to the other.

2. Make two vertical cuts (from the horizontal cut) approximately 3 inches (76.2 mm) long, at both sides of the joint.

3. Place a 1-inch (25.4 mm) mark on the sealant tab as shown in the illustration.

4. Grasp the 2-inch (50.8-mm) piece of sealant firmly just beyond the 1-inch (25.4 mm) mark and pull at a 90° angle.

5. If dissimilar substrates are being sealed, check the adhesion of sealant to each substrate separately. This is accomplished by extending the vertical cut along one side of the joint, checking adhesion to the opposite side and then repeating for the other surface.

6. The adhesion test is considered passing when 1 inch (25.4 mm) of sealant is elongated to 4 inches (101.6 mm) without bond loss.

How to Use Dow Corning Silicone Pavement Sealants

Cure Characteristics Dow Corning silicone pavement sealants cure by reacting with atmospheric moisture, but the rate of cure is dependent on temperature and humidity. At a temperature of 75°F (24°C) and relative humidity of 50 percent, Dow Corning 888 Silicone Joint Sealant will cure to a tack-free surface in one hour or less and reach its ultimate properties in 7 to 14 days. Temperatures of 100°F (38°C) will reduce the tack-free time to about 30 minutes, and ultimate properties of the sealant could be reached in just a few days of continuous exposure. Conversely, low temperatures will reduce the cure rate and increase the time required for the sealant to become tack-free. For example, at 40°F (4°C) the tack-free time will be about two to three hours. At a temperature of 75°F (24°C) and a relative humidity of 50 percent, Dow Corning 890-SL Self-Leveling Silicone Joint Sealant will skin over in about 40 minutes. The self-leveling sealant will reach its ultimate properties in 14 to 21 days. Dow Corning silicone pavement sealants will cure slightly faster at higher temperatures and slower at lower temperatures.

While it may require days for the sealant to reach ultimate properties, roads or runways may be quickly reopened to traffic, often within minutes of sealant placement, provided that the sealant is properly recessed. When sealant is placed in new pavement or in resealing jobs where there is no excessive faulting or slab deflection (vertical movement), the roadway may be opened to traffic as soon as a skin forms on the sealant.

Where excessive faulting or vertical deflection occurs as a result of traffic, the sealant should be allowed to sufficiently cure and develop integrity before the road or runway is reopened. The time required to develop integrity will depend on several factors, such as the amount of vertical movement, the time of year, temperature and humidity, and the sealant being used.

Allow the sealant to develop sufficient integrity to resist being forced from a joint by a backer rod that is pumped upward by traffic movement. This problem occurs occasionally in the cooler spring or fall months on older pavement without load transfer devices or aggregate interlock.

Once cured, Dow Corning silicone pavement sealants have the capability to withstand a high degree of extension and compres-sion with no loss of bond.

Joint Design Good sealant installation begins with good joint design – and anticipated movement is a key design consideration. While the high-movement capability of Dow Corning silicone sealants provides added safety when anticipated and actual movements differ, proper design and correct installation procedures will maximize performance.

Joint Width Joints may be either sawed or formed to the required dimen-sions. The minimum joint width recommended for Dow Corning silicone pavement sealants is 1/4 inch (6.35 mm). But a 3/8-inch (9.53-mm) width is generally preferred for faster sealant installation.

Transverse joints must be wide enough to prevent excessive movement. A 1/4-inch (6.35-mm) wide joint with 20-foot (6-m) spacing may be satisfactory in a warm climate, but more severe climates with wide temperature ranges or less frequent spacing will require a wider joint. Joint spacing, the coefficient of thermal expansion of the pavement, expected temperature range, and the anticipated temperature at time of sealing must all be considered.

The joints should be sized so that the maximum extension and compression do not exceed +100 and -50 percent respectively.

This sizing should include a safety factor of two or three to allow for non-uniformity of joint movement two to three slabs working in unison. The time of year (spring, summer, fall) should also be considered.

Figure 2 – Joint Design Considerations: Dow Corning 888 Silicone Joint Sealant

Good Design Joint width wide enough to accommodate movement.

Sealant tooled to a minimum of 3/8 inch (9.53 mm) below pavement surface.

Proper backer rod selected and placed correctly.

Joint sawed deep enough to allow correct placement of backer and sealant.

Sufficient room for debris in joint to pump up and not disturb the new sealant.

Poor Design Sealant not tooled to proper depth.

Sealant bead too thick; wrong width-to-depth ratio.

No backer rod; results in bead too thick and no support to tool against; conse-quently, sealant makes minimal contact with joint walls.

No backer rod; results in sealant bonding to bottom of joint; joint too shallow.

Figure 3- Joint Design Considerations: Dow Corning 890-SL Self-Leveling Silicone Joint Sealant

Good Design Joint width wide enough to accommodate movement.

Sealant recessed* a minimum of 3/8 inch (9.53 mm) below pavement surface.

Proper backer rod selected and placed correctly.

Joint sawed deep enough to allow correct placement of backer and sealant.

Sufficient room for debris in joint to pump up and not disturb the new sealant.

Poor Design

Sealant not recessed to proper depth.

Sealant bead too thick; wrong width-to-depth ratio.

No backer rod; results in bead too thick;

sealant bonding to bottom of joint.

*Recess if measured from the highest point of the installed backer material to the lowest point of the pavement surface at the joint wall.

Joint Depth The joint must be deep enough to allow proper placement of the sealant and a bond breaker/backer rod. Minimum depth requirements will vary slightly depending on joint width (see Table 1 on Page 18).

Experience has shown that better performance of Dow Corning silicone pavement sealants can be obtained by maintaining a recess of 3/8 inch (9.53 mm) or greater. It is especially important to maintain the proper recess as the joint width approaches and/or exceeds one inch. Dow Corning recommends the following recess guidelines:

Joint Width Recess

1/4 to 1-1/4 inches 3/8 inch (6.35 to 31.8 mm) (9.53 mm)

Greater than 1-1/4 inches 1/2 inch (Greater than 31.8 mm) (12.7 mm)

Joint Preparation Obtaining the desired performance depends upon using correct installation procedures. All contaminants, especially dried laitance from saw-cutting and previous sealants, must be removed with a high pressure water wash followed by a sand blast. Leaving materials of this type on the surface of the joint face will prevent development of a good adhesive bond. A clean joint will have no visible signs of residual sealant or debris on the joint wall, and will leave no residual cement powder or dust on your fingers after rubbing the joint face.

Dow Corning 888 Silicone Joint Sealant will not bond to wet concrete. Dow Corning 890-SL Self-Leveling Silicone Joint Sealant will not bond to wet asphalt or concrete. Moisture in and on the pavement is difficult to detect. The pavement MUST be allowed to dry. When in doubt, it is wiser to allow additional drying time than to risk sealant adhesion failure.

JOINT FACES MUST BE CLEAN, DRY AND FROST-

FREE WHEN THE SEALANT IS INSTALLED.

After drying, it is especially important that the top 1 inch (25.4

mm) of each joint face be sandblasted. When sandblasting, follow all federal, state and local laws and/or regulations regarding the proper use and handling of equipment. The primary purpose is to remove traces of residual laitance. The sandblasting nozzle must be held at an angle to the joint face and within 1 or 2 inches (25.4 or 50.8 mm) of the pavement. Pointing it toward the bottom of the joint or at too great a distance from the face allows the force of the blast to dissipate ineffectively. These points and others regarding surface preparation of new and old concrete pavement are expanded upon in following sections.

Backer Rod Selection Another essential element in good joint design is use of a bond breaker/backer rod. A primary function of the backer rod is to act as a bond breaker, preventing three-sided adhesion of the sealant while at the same time forming the desired cross section of the sealant bead. Failure to utilize a backer rod will allow the sealant to bond to the bottom of the joint. This results in excessive stress on the sealant.

Another function of the backer rod is to control the thickness of the sealant bead. The backer rod should be approximately 25 percent oversized so that it fits tightly into the joint. A loose backer rod will be pushed deeper into the joint when the sealant is installed and will not provide adequate support for proper tooling of Dow Corning 888 Silicone Joint Sealant. Thus, the thickness of the sealant bead cannot be controlled as required. With proper tooling, Dow Corning 888 Silicone Joint Sealant is pushed down onto the backer rod and firmly against the joint walls, resulting in intimate contact, proper wetting and good adhesion with the joint walls. Dow Corning 890-SL Self-Leveling Silicone Joint Sealant requires a tight-fitting backer rod to control thickness of the sealant bead and to prevent the sealant from bypassing the backer rod to the bottom of the joint.

Failure to use a backer rod, or use of the wrong material, will nearly always result in failure or reduced performance of the sealant. Dow Corning recommends the use of a closed cell, expanded polyethylene foam rod for general use with Dow Corning silicone pavement sealants. Where the joints are irregular, bond breakers such as Sof Rod ™* help prevent the self-leveling sealants from bypassing the backer rod and allow the sealants to enter the bottom of the joint. In all cases, the backer rod must be oversized so that it fits tightly in the joint.

Sealant and Backer Rod Placement Depths

The sealant bead must be placed a minimum of 3/8 inch (9.53

mm) below the pavement surface. The sealant bead should be a minimum of 1/4-inch (6.35-mm) thick but should not be greater than 1/2-inch (12.7-mm) thick. A width-to-depth ratio of 2:1 is ideal and should be maintained throughout the bead whenever possible.

Based on these values, the top surface of the backer rod is typically positioned so that it is between 5/8 inch (15.9 mm) and 7/8 inch (22.2 mm) below the pavement surface. If other operations, such as diamond grinding, are to be done after sealant placement, the sealant recess and the resulting joint depth and backer rod placement must be increased.

*Sof Rod is a trademark of Applied-Extrusion Technologies.

Sealing New Concrete Pavement

Before attempting to seal joints in new concrete, the concrete must be given plenty of time to cure, dry and develop strength such that the joint reservoir can be sawn without concrete damage (i.e., raveling, spalling, etc.). The time between sawing of the initial cut (contraction cut to control cracking) and the joint sealant reservoir will depend upon such factors as mix design (i.e., conventional, Fast Track, High Early Concrete mixes), cement type, time of year concrete is placed, temperature, etc.

Only clean and dry joints should be sealed.

For conventional concrete mixes, it is recommended that the concrete be allowed to cure and dry a minimum of 7 days in good drying weather before installing Dow Corning silicone pavement sealants. Cold, wet, inclement weather will require a longer drying time. An additional day of good drying weather should be allowed for each day of poor drying weather.

Dow Corning silicone pavement sealants have been successfully used in many Fast Track and High Early Concrete applications. Because of the continued introduction of new methods and mix types, please contact your Dow Corning representative for current recommendations in these applications.

Joint sealant reservoirs are prepared by saw-cutting (i.e., diamond blades) the concrete to the specified width and depth. It is recommended that freshly sawed joints be washed with high pressure water immediately after sawing to remove most of the saw slurry from the joint faces. Joint washing should be in one direction (working forward) to minimize recontamination.

After the joints have dried, the joints should be sandblasted to remove residual laitance from the joint walls. Sandblasting should be done in two passes, one for each face, with the nozzle held at an angle to the joint face and within 1 or 2 inches (25.4 or 50.8

mm) of the pavement. Sandblasting should be done to the depth at which the sealant and backer rod are to be installed.

Experience has shown that the best method for removing contaminants is by sandblasting the dry joint that was previously flushed with water after the saw-cutting process. Other techniques, such as grinding or wire-brushing, are not recommended. They have been found to be less effective due to possible operator error and/or equipment problems. If conditions are such that sandblasting is not permitted, high pressure waterblasting may be used as an alternative. Contact your Dow Corning representative BEFORE attempting to use this joint cleaning method to discuss the appropriate procedures.

After sandblasting, the sand, as well as any dust and dirt deposited by wind and traffic, must be blown out of the joint and away from the area around it using a high-pressure air blast. As with the water wash, the air blast should move in only one direction (forward) to prevent recontamination of the joint.

Compressed air, at a pressure of at least 90 psi (620 kPa), should be used to blow out the joint just before installation of the backer rod. Air compressors used for this purpose must be equipped with traps capable of providing moisture-free and oil-free air.

Just before the backer rod is installed into the joint, rub your finger across the dry joint face to determine that residual dust or dirt has been removed. If joints still contain dust or dirt, these contaminants must be removed before backer rod and sealant installation.

Solvents should not be used to remove oils, because they generally only carry the materials further into the concrete pores or spread them over the surface.

NOTE: Many new concrete additives are being sold to the highway industry that allow concrete to be placed and opened to traffic in record time. These materials may be additives to or substitutions for Portland Cement Concrete. When using any of these new materials, adhesion testing of Dow Corning silicone pavement sealants is required. To test adhesion, submit samples of the material to Dow Corning at least 30 days before anticipated use. Dow Corning will test the material and provide you with specific recommendations.

Resealing Old Concrete Pavement

The installation techniques required for resealing can be summarized as removal of old sealant/seal, proper cleaning of the joint, and installation of the bond breaker and sealant.

The tools and techniques used to remove the existing sealant or joint filler will be determined by the material in the joint and by available equipment. The old sealant can be removed by cutting and/or saw-cutting, which slightly widens the joint to produce a new surface for sealing. Some materials, compression seals for example, are simply pulled out of the joint and then sandblasted to remove the lubricant/adhesive.

After removing previous materials, immediately high-pressure water wash the joint to remove sawing residue. Wash in one direction (forward) to prevent recontamination. When the joint has dried, it should be sandblasted to remove any residual dust using techniques described previously.

After sandblasting, the joint should be blown out with compressed air at a pressure of 90 psi (620 kPa) to remove sand and dust. Air should be free of oil and water.

As a final check before bond breaker and sealant installation, the joints should be inspected for residual dust and/or old sealing material. If dust or old sealing material remain, these contaminants should be removed using techniques described previously.

Table 1 – Theoretical Estimating Requirements*

Jo in t W id th , i nc he s

S ea la nt

B ea d T hi ck ne ss

, i nc he s

M in im um

J oi nt D ep th

, i nc he s

B ac ke r R od D ia m et er in ch es

B ac ke r

R od

D ep th , i nc he s

0-

S L

*Installation yields (linear feet/gallon) are based on calculations for an exact sealant bead shape-factor. Actual yield will vary depending on deviation from calculated bead shape, tooling techniques, backer material placement, waste, and applicator experience.

Estimated Coverage (linear feet/gal.)

1/4 1/4 1-1/8 3/8 5/8 246 275

3/8 1/4 1-3/8 1/2 5/8 149 173

1/2 1/4 1-3/8 5/8 5/8 103 123

5/8 5/16 1-5/8 3/4 11/16 66 83

3/4 3/8 1-7/8 1 3/4 46 60

7/8 7/16 2 1 13/16 33 45

1 1/2 2-1/8 1-1/4 7/8 26 35

>1 1/2 >2-1/8 1-1/4+ 1 – –

Table 2 – Metric Estimating Equivalents*

*1 inch = 25.4 millimeters, 1 gallon = 3.79 liters.

Installation yields (linear meters/liter) are based on calculations for an exact sealant bead shape-factor. Actual yield will vary depending on deviation from calculated bead shape, tooling techniques, backer material placement, waste, and applicator experience.

Jo in t W id th , m m

S ea la nt

B ea d T hi ck ne ss

, m m

M in im um

J oi nt D ep th

, m m

B ac ke r

R od

D ia m et er , m m

B ac ke r

R od

D ep th , m m

0-

S L

Estimated Coverage (linear meters/liter)

6.35 6.35 28.6 9.53 15.9 19.8 22.1

9.53 6.35 34.9 12.7 15.9 12.0 13.9

12.7 6.35 34.9 15.9 15.9 8.3 9.9

15.9 7.94 41.3 19.1 17.5 5.3 6.7

19.1 9.53 47.6 25.4 19.1 3.7 4.8

22.2 11.1 50.8 25.4 20.6 2.6 3.6

25.4 12.7 54 31.8 22.2 2.1 2.8

>25.4 12.7 >54 31.8+ 25.4 – –

Full Depth Asphalt Pavements

NOTE: Only Dow Corning 890-SL Self-Leveling Silicone Joint Sealant is recommended for sealing joints in asphalt pavements.

Sealing New Asphalt Pavements Before attempting to seal joints in new asphalt, the asphalt must be given sufficient time to cool and to cure, so that damage will not result from sawing. This time will depend upon a number of factors, such as mix design, time of year for placement, geographic location, and past experiences. The asphalt must also be completely dry prior to sealant installation.

Joints should be prepared by saw-cutting (i.e., diamond blades) to the specified width and depth. Routers (i.e., impacting devices) should not be used, as routing of asphalt pavements can cause damage to the pavement, which in turn leads to poor joint performance. In new construction, a shallow cut is recommended where the backer material is placed on the bottom of the joint. A shallow cut saves time and saw blades. All joints to be sealed must be sound, clean, dry and frost-free.

Freshly sawed joints should be washed with water immediately after sawing to remove any loose material from the joint faces. Joint washing should be in one direction (forward) to prevent or minimize recontamination. Any contaminants remaining on the surface of the joint wall may prevent development of a good bond.

Experience has shown that the best method for removing contaminants is by sandblasting (sand cleaning) the dry joint that was previously flushed with high-pressure water after the saw-cutting process. Other techniques, such as grinding, wire-brushing, or routing have been found to be less effective and may cause damage to the joint.

Sandblasting should be done in two passes, one for each face, with the nozzle held at an angle to the joint face and within 1 or 2 inches (25.4 or 50.8 mm) of the pavement. Sandblasting should be done to the depth at which the sealant and backer material are to be installed. The sand, as well as dust and dirt deposited by wind and traffic, must be blown out of the joint and away from the area around it using a high-pressure air blast. The air blast should move in only one direction (forward).

Compressed air, at a pressure of at least 90 psi (620 kPa), should be used to blow out the joint just before installation of the backer rod. Air compressors used for this purpose must be equipped with traps capable of providing moisture-free and oil-free air.

Just before actual sealing of the joint, rub your finger across the dry joint face to determine that residual dust has been removed. If joints still contain dust or dirt, these contaminants must be removed before backer rod and sealant installation.

Resealing Old Asphalt Pavements All old sealant and/or joint filler must be removed prior to sealant installation. The tools and techniques used to remove the existing sealant or joint filler will be determined by the material in the joint and by available equipment. The old sealant typically can be removed by cutting, plowing and/or saw-cutting, which also widens the joint to the required dimensions. Residue from sawing (i.e., wet sawing) of asphalt and any old caulk or sealant material still remaining on the joint face must be removed before backer rod placement and resealing. As discussed in previous sections, any debris and residue left by the wet sawing operation must be removed by an immediate high-pressure water wash. This is followed, after drying, by sandblasting (i.e., sand cleaning) using techniques described previously.

After sandblasting, the joint is blown out with compressed air to remove final dust and dirt from the previous step and any dust and dirt that may have been blown in by traffic, wind, etc. The compressed air is supplied from a compressor equipped with traps to provide oil-free and water-free air at a minimum of 90 psi (620 kPa).

As a final check prior to installing backer material and sealant, the joints should be checked to ensure that joints are dry and no residual dust remains. This is accomplished by rubbing your finger along the joint face to examine for dust. If dust is present, it must be removed before proceeding with backer material installation.

Asphalt Overlays

NOTE: Only Dow Corning 890-SL Self-Leveling Silicone Joint Sealant is intended for sealing joints in asphalt pavements.

Sealing Joints in New Asphalt Overlays It is recommended that joints in fresh asphalt be sawn (i.e., diamond blades) after the asphalt has cooled and “cured” such that sawing does not damage the asphalt joint (i.e., raveling). The joints should be centered DIRECTLY OVER the concrete joints below. To control cracking, it is common practice to carefully saw these joints to a depth of 1/2 of the total asphalt thickness. Then the sealant reservoir should be sawed to proper dimensions. Joint dimensions should be as per state specifications.

As discussed previously, the joint must be free of moisture, sawing residues, dirt, dust, etc., prior to sealant installation. The removal techniques have been described in previous sections.

Sealing Reflection Cracks in Older Asphalt Overlays

When Dow Corning 890-SL Self-Leveling Silicone Joint Sealant is used for sealing reflection cracks in older asphalt pave-ments, additional joint preparation steps must be used. Cracks that have formed in the asphalt pavement must be totally removed by saw-cutting.