Slurry Seals

Slurry Seals were used for the first time in Canada in the 1960s and their usage has exponentially increased across Canada where approximately 3.5 million square metres are now placed every year. Slurry Seal systems are used as preventive maintenance treatments.

Slurry Seals are properly proportioned mixtures of unmodified cationic emulsified asphalt, mineral aggregates, mineral filler, water and additives which are mixed and spread with a machine over a properly prepared surface. A slurry mixture forms an impervious thin overlay over an existing pavement. The aggregate is relatively fine (less than 6.3 mm) and always 100% crushed. The fines content ranges from 8% to 12% and the residual bituminous binder is generally between 9.0% and 10%. The application rate for a typical bituminous pavement ranges between 6.5 and 7.0 kg/m2.

Slurry Seals are treatments that provide pavement sealing and pavement texture but are not appropriate to resolve structural pavement deficiencies. These systems are well suited as a preventive maintenance treatment to extend the life of structurally sound low traffic volume pavements. Preventive maintenance treatments are low-cost treatments that retard deterioration of the pavement, maintain or improve the functional condition of the roadway, and extend the pavement's service life when applied on suitable candidates.

Surface slurry sealing systems are surface treatments that provide protection of the pavement surface by delaying the appearance of surface defects caused by both the environment and the associated oxidization of the existing surface. Oxidization of the bituminous surface material leads to surface defects such as raveling, potholes, as well as thermal and age cracking. By sealing the pavement using a Slurry Seal, the rate at which the existing bituminous surface material oxidizes is greatly reduced. Slurry Seal systems are binder rich mixtures (between 8.0% and 10.0% bitumen), which waterproof and seal existing surfaces, protecting the pavement from the adverse environmental effects.

As for any other roadway material, the selection of good quality components is a key element in the performance of Slurry Seals. However, it is important to point out that the selection of high quality components alone may not be sufficient to ensure that the combination of all the components will provide satisfactory performance. Good quality components are not always compatible with one another. Mixture testing to ensure compatibility of the primary components is therefore critical to ensure that the Slurry Seal systems will work adequately.

The mixing and the placement of Slurry Seals are performed simultaneously using a slurry machine. Slurry machines are fitted with the following components:

• Storage bins and tanks for aggregate, emulsion, water, mineral filler and field additives
• A pugmill unit for the mixing of the slurry
• A spreader box for the placement of the slurry

There are two types of machines used to mix and place Slurry Seal systems: truck mounted machines and self-propelled continuous feed machines. The truck mounted machines are loaded with water, emulsion and aggregates supplied at a central location while the self-propelled continuous feed machines are capable of receiving materials from special nurse units while continuing to mix and apply the mixture.

The performance of surface slurry sealing systems may be evaluated in terms of various aspects of road engineering but are predominantly classified as pavement sealers. The service life extension of a pavement treated with slurry seal ranges from 4 to 8 years, depending on the condition of the existing pavement and the volume of traffic. Slurry Seals are generally used on low volume roads.

The concept of pavement preservation (as opposed to existing strategies of reactive treatments and reconstruction) is gaining acceptance in North America. The pavement preservation concept advocates the improvement of the overall condition of road networks rather than that of a single road at a time. The use of preventive maintenance treatments is an essential part of a pavement preservation strategy. Hence, the use of Slurry Seals on low volume roads to preserve pavements is becoming the preferred choice by many North American road agencies.

• Ontario