FOOTWAY SLURRY SEALING BY PICTURES

INTRODUCTION
Please do not be mislead by what may appear to be a "rough and ready process", IT IS NOT !

Considerable attention to detail is needed to produce a good slurry seal surface, and a great deal of knowledge and experience is needed to make those slight adjustments for things such as weather conditions, ambient temperature and slight differences in the moisture content of the dust.

In my experience good footway slurry seal surfacing is more "gang" dependent than company dependent, by which I mean just because you have good work from one company one year you will not necessarily receive the same standard of work the following year..
But I have found that if you have the same gang you had the year before it is likely you will obtain the same standard of work, and the good gangs are usually "known" and in demand.
This process, performed correctly, is an excellent cost effective surfacing. It is regarded as a preventative maintenance process which will prolong the life of a footway that is in sound structural condition, it is not able to strengthen a footway that has failed structurally.
As always I am going to recommend  strong site supervision to ensure good quality work. 
Slurry seal and its production is/was described in 

BS 434-1 : 1984 : Bitumen road emulsions (anionic and cationic)
Part 1 : Specification for bitumen road emulsions
This part specifies the properties of various types of emulsion and the various types of test to determine these properties.
and
BS 434-2 : 1984 : Bitumen road emulsions (anionic and cationic)
Part 2 : Code of practice for use of bitumen road emulsions
This former edition described the uses of bitumen emulsions, and specified/recommended the way in which they where to be used. e.g. surface dressing, emulsion macadams, slurry sealing, etc..

There has recently been issued a new edition of BS 434:Part 2, this new edition, 
BS 434-2 : 2006 : Code of Practice for the use of cationic bitumen road emulsions on roads and other paved areas
may lack some of the precise detail that the superseded copy contained, but it is an excellent document and I would suggest you obtain a copy as it contains a wealth of useful information relevant to the successful use of bitumen emulsion in many highways maintenance applications.

I am not aware if BS 434-1:1984 has yet been superseded.

I would also suggest you retain your "old" standards, as a reference documents, particularly as a guide to the production of slurry seal mixtures, should you wish to produce small amounts yourself, although suppliers of the bitumen emulsions are usually prepared to help in the design of appropriate slurry seals and slurry macadams if you will be buying reasonable amounts of their emulsion.

CONTENTS

Mixing and Applying the Slurry Seal
Materials Required for Slurry Sealing
Bitumen Emulsion and Retard Agent ("Dope")
Applying the Slurry
Spreading the Slurry Evenly
Finished Surface of a Typical Footway Slurry Seal Surface
Surface Finishing and Setting Time
Poor Quality Slurry Sealing

THE PRINCIPLES OF SLURRY SEALING

Mixing and Applying the Slurry Seal

The aggregate, pre-wet water, cement, dope and lastly the bitumen emulsion have all been added to the mixer and mixed until there is a thorough mixing of components before discharging onto the footway for screeding.

Materials required for Slurry Sealing Lorry showing the materials needed to carry out footway slurry sealing. This will include the coarse aggregate ("dust"), the bitumen emulsion, the retard agent ("dope"), and the cement. Please note all the various size containers for the accurate proportioning of the slurry.

The electro-negativity of the aggregate source is very important in the process of slurry sealing using cationic bitumen emulsion, you must be aware of this characteristic and understand that it is not just a question of buying "dust" that has the correct grading, the surface of the aggregate particles must also exhibit a significant negative charge.

Applying the Slurry

Spreading the Slurry Evenly

Finished Surface of a Typical Footway Slurry Seal

Surface Finishing and Setting Time

After initial screeding to distribute the slurry evenly over the footway it is "brushed" to establish a uniform thickness and appearance to the final surface.
At a reasonable ambient temperature (ten degrees centigrade) it will be approximately one hour before it is safe to walk on, with care.
It will be several hours before it is fully "set".

For an explanation of the Footway Slurry Sealing process, Press -------> HERE

POOR QUALITY SURRY SEALING

I include this section as much to support those contractors who carry out good work as to encourage others to improve, and to give guidance to those who are responsible for overseeing this type of footway refurbishment.
Slurry sealing is an excellent, cost effective, preventative maintenance process for the highways maintenance engineer to employ where footways are structurally sound but the surface is beginning to fret through bitumen oxidation and general wear and tear.
I would not want to see the process lost because of occasional poor quality. 

Below are pictures of how slurry sealing should NOT be carried out. 
You will note that, for whatever reason, the coarser component of the slurry seal aggregate has been "pulled out" / segregated from the matrix of the slurry seal layer, leaving a rough none uniform surface. 
This segregated material is likely detach from the surface leaving loose aggregate on the footway, and you will note some areas that have little if any coarser aggregate cover.

Possible causes of low quality surfacing such as this are :-
1) The aggregate did not meet the specification, in that it had a proportion of large, above the specification limit, aggregate
2) The aggregate was poorly graded, in that it had a larger proportion of the permissible larger aggregate sizes than the specification allows. 
3) Operatives trying to achieve a larger coverage from a given amount of slurry than a particular formulation will allow without segregation. The slurry should be laid at a thickness that allows the coarser aggregate component to be accommodated in the thickness of the layer to produce a uniform appearance to the surface.  
If you require a satisfactory thinner layer it is necessary to use a different aggregate grading.
4) Inexperienced operatives who have not received correct training.

A great deal of advice and guidance on the various uses of Bitumen Emulsion, can be obtained from :- 
The Road Emulsion Association Limited,
including a large number of "DataSheets".

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