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Introduction

Curing is the process of controlling the rate and extent of moisture loss from concrete during cement hydration. It may be either after it has been placed in position (or during the manufacture of concrete products), thereby providing time for the hydration of the cement to occur. Since the hydration of cement does take time – days, and even weeks rather than hours – curing must be undertaken for a reasonable period of time if the concrete is to achieve its potential strength and durability. "Curing is the process of controlling the rate and extent of moisture loss from concrete during cement hydration."  Curing may also encompass the control of temperature since this affects the rate at which cement hydrates.

The curing period may depend on the properties required of the concrete, the purpose for which it is to be used, and the ambient conditions, ie the temperature and relative humidity of the surrounding atmosphere. Curing is designed primarily to keep the concrete moist, by preventing the loss of moisture from the concrete during the period in which it is gaining strength. Curing may be applied in a number of ways and the most appropriate means of curing may be dictated by the site or the construction method.

Curing by preventing excessive loss of moisture from the concrete: either by

• leaving formwork in place
• covering the concrete with an impermeable membrane after the formwork has been removed
• by the application of a suitable chemical curing agent (wax etc)
• or by a combination of such methods n Curing by continuously wetting the exposed surface thereby preventing the loss of moisture from it. Ponding or spraying the surface with water are methods typically employed to this end.

Effect of duration of curing on properties of concrete

The strength of concrete is affected by a number of factors, one of which is the length of time for which it is kept moist, ie cured. Figure 1 illustrates this, comparing the strength (at 180 days) of concrete for which the surfaces have been:

• kept moist for 180 days;
• kept moist for various periods of time and allowed to dry out; and
• allowed to dry out from the time it was first made. As may be seen in this example, concrete
• allowed to dry out immediately achieves only 40% of the strength of the same concrete water cured for the full period of 180 days. Even three days water curing increases this figure to 60%, whilst 28 days water curing increases it to 95%. Keeping concrete moist is therefore, a most effective way of increasing its ultimate strength. Concrete that is allowed to dry out quickly also undergoes considerable early age drying shrinkage. Inadequate or insufficient curing is one of main factors contributing to weak, powdery surfaces with low abrasion resistance. The durability of concrete is affected by a number of factors including its permeability and absorptivity. Broadly speaking, these are related to the porosity of the concrete and whether the pores and capillaries are discrete or interconnected. Whilst the number and size of the pores and capillaries in cement paste are related directly to its water-cement ratio, they are also related, indirectly, to the extent of water curing. Over time, water curing causes hydration products to fill, either partially or completely, the pores and capillaries present, and, hence, help to reduce the porosity of the paste.  

Figure 2 illustrates the effect of different periods of water curing on the permeability of cement paste. As may be seen, extending the period of curing reduces the permeability. 

Curing Methods

General Methods of curing concrete fall broadly into the following categories:

• Those that minimise moisture loss from the concrete, for example by covering it with a relatively impermeable membrane.
• Those that prevent moisture loss by continuously wetting the exposed surface of the concrete.
• Those that keep the surface moist and, at the same time, raise the temperature of the concrete, thereby increasing the rate of strength gain. This method is typically used for precast concrete products and is outside the scope of this data sheet. 

Impermeable-membrane

Curing Formwork - Leaving formwork in place is often an efficient and cost-effective method of curing concrete, particularly during its early stages. In very hot dry weather, it may be desirable to moisten timber formwork, to prevent it drying out during the curing period, thereby increasing the length of time for which it remains effective.

It is desirable that any exposed surfaces of the concrete (eg the tops of beams) be covered with plastic sheeting or kept moist by other means. It should be noted that, when vertical formwork is eased from a surface (eg from a wall surface) its effectiveness as a curing system is significantly reduced.

Plastic sheeting - Plastic sheets, or other similar material, form an effective barrier against water loss, provided they are kept securely in place and are protected from damage. Their effectiveness is very much reduced if they are not kept securely in place. The movement of forced draughts under the sheeting must be prevented.

They should be placed over the exposed surfaces of the concrete as soon as it is possible to do so without marring the finish. On flat surfaces, such as pavements, they should extend beyond the edges of the slab for some distance, eg or at least twice the thickness of the slab, or be turned down over the edge of the slab and sealed.

For flat work, sheeting should be placed on the surface of the concrete and, as far as practical, all wrinkles smoothed out to minimise the mottling effects (hydration staining), due to uneven curing, which might otherwise occur. Flooding the surface of the slab under the sheet can be a useful way to prevent mottling. Strips of wood, or windrows of sand or earth, should be placed across all edges and joints in the sheeting to prevent wind from lifting it, and also to seal in moisture and minimise drying.

For decorative finishes or where colour uniformity of the surface is required sheeting may need to be supported clear of the surface if hydration staining is of concern. This can be achieved with wooden battens or even scaffolding components, provided that a complete seal can be achieved and maintained.

For vertical work, the member should be wrapped with sheeting and taped to limit moisture loss. As with flatwork, where colour of the finished surface is a consideration, the plastic sheeting should be kept clear of the surface to avoid hydration staining.

Care must also be taken to prevent the sheeting being torn or otherwise damaged during use. A minimum thickness is required to ensure adequate strength in the sheet; ASTM C 171 Sheet Materials for Curing Concrete specifies 0.01 mm. Figure 3 illustrates the lack of effectiveness of plastic sheeting with holes equivalent to only 1.7% of the sheet’s surface area.

Plastic sheeting may be clear or coloured. Care must be taken that the colour is appropriate for the ambient conditions. For example, white or lightly coloured sheets reflect the rays of the sun and, hence, help to keep concrete relatively cool during hot weather. Black plastic, on the other hand, absorbs heat to a marked extent and may cause unacceptably high concrete temperatures. Its use should be avoided in hot weather, although in cold weather its use may be beneficial in accelerating the rate at which the concrete gains strength.

Clear plastic sheeting tends to be more neutral in its effect on temperature (except in hot weather, where it fails to shade the surface of the concrete) but tends to be less durable than the coloured sheets, thereby reducing its potential for re-use.

Membrane-forming curing compounds - Curing compounds are liquids which are usually sprayed directly onto concrete surfaces and which then dry to form a relatively impermeable membrane that retards the loss of moisture from the concrete. Their properties and use are described in AS 3799 Liquid Membrane-forming Curing Compounds for Concrete.

They are an efficient and cost-effective means of curing concrete and may be applied to freshly placed concrete or that which has been partially cured by some other means. However, they may affect the bond between concrete and subsequent surface treatments. Special care in the choice of a suitable compound needs to be exercised in such circumstances. The residue from some products may prevent the adhesion of flooring products and tiles onto the concrete surface.

Curing compounds are generally formulated from wax emulsions, chlorinated rubbers, synthetic and natural resins, and from PVA emulsions. Their effectiveness varies quite widely, depending on the material and strength of the emulsion, as is illustrated in Figure 4. Note: Attention should be drawn to the very poor efficiency of PVA curing compounds.

When used to cure fresh concrete, the timing of the application of the curing compounds is critical for maximum effectiveness. They should be applied to the surface of the concrete after it has been finished, as soon as the free water on the surface has evaporated and there is no water sheen visible. Too early an application dilutes the membrane; too late results in it being absorbed into the concrete, with a consequent failure of the membrane to form.

They may also be used to reduce moisture loss from concrete after initial moist curing or the removal of formwork. In both cases, the surface of the concrete should be thoroughly moistened before the application of the compound to prevent its absorption into the concrete.

The use of curing compounds will not prevent formation of early age thermal cracking.

Curing compounds can be applied by hand spray, power spray, brush or roller. The type or grade of curing compound should be matched to the type of equipment available and the manufacturer’s directions followed. The rate of application should be uniform, with coverage normally in the range 0.20 to 0.25 litres/m2. Where feasible, two applications at right angles to each other will help ensure complete coverage.

Pigmented compounds also help ensure complete coverage and are advantageous in helping concrete surfaces reflect rather than absorb heat. Figure 5 shows pressure spraying of a whitepigmented curing compound.

It is extremely important to check the subsequent floor finish. Most curing compounds must be removed before the application of any applied floor finishes such as direct stick carpet and vinyl, epoxy or polyurethane coatings and ceramic tile adhesives.

Finally, it should be noted when using curing compounds that are solvent-based adequate ventilation must always be provided in enclosed spaces and other necessary safety precautions taken. Manufacturer’s recommendations should always be followed.

Internal curing compounds - These are incorporated into the concrete as an admixture hence known as internal curing compounds. They inhibit moisture loss and thereby improve long term strength and reduce drying shrinkage. Internal curing compounds are relatively new and care should be taken when utilised. They have been used in tunnel linings and underground mines to provide at least partial curing when traditional methods are difficult or even impossible to employ.

Water Curing

General - Water curing is carried out by supplying water to the surface of concrete in a way that ensures that it is kept continuously moist.

The water used for this purpose should not be more than about 5°C cooler than the concrete surface. Spraying warm concrete with cold water may give rise to ‘thermal shock’ that may cause or contribute to cracking.Alternate wetting and drying of the concrete must also be avoided as this causes volume changes that may also contribute to surface crazing and cracking.

Ponding - Flat or near-flat surfaces such as floors, pavements, flat roofs and the like may be cured by ponding. A ‘dam’ or ‘dike’ is erected around the edge of the slab and water is then added to create a shallow ‘pond’ as shown in Figure 6. Care must be taken to ensure the pond does not empty due to evaporation or leaks.

Ponding is a quick, inexpensive and effective form of curing when there is a ready supply of good ‘dam’ material (eg clay soil), a supply of water, and the ‘pond’ does not interfere with subsequent building operations. It has the added advantage of helping to maintain a uniform temperature on the surface of the slab. There is thus less likelihood of early age thermal cracking in slabs that are cured by water ponding.

Sprinkling or fog curing - Using a fine spray or fog of water can be an efficient method of supplying additional moisture for curing and, during hot weather, helps to reduce the temperature of the concrete.

As with other methods of moist curing, it is important that the sprinklers keep the concrete permanently wet. However, the sprinklers do not have to be on permanently; they may be on an intermittent timer.

Sprinklers require a major water supply, can be wasteful of water and may need a drainage system to handle run-off. The alternative is to have a ‘closed’ system where the water is collected and recycled.

Sprinkler systems may be affected by windy conditions and supervision is required to see that all of the concrete is being kept moist and that no part of it is being subjected to alternated wetting and drying. This is not easy to achieve.

Wet coverings - Fabrics such as hessian, or materials such as sand, can be used like a ‘mulch’ to maintain water on the surface of the concrete. On flat areas, fabrics may need to be weighed down. Also, it is important to see that the whole area is covered. Wet coverings should be placed as soon as the concrete has hardened sufficiently to prevent surface damage. They should not be allowed to dry out as they can act as a wick and effectively draw water out of the concrete.

Fabrics may be particularly useful on vertical surfaces since they help distribute water evenly over the surface and even where not in contact with it, will reduce the rate of surface evaporation. Care should be taken however, that the surface of the concrete is not stained, perhaps by impurities in the water, or by the covering material.

New fabrics can leach fabric stains, pre‑washing should be essential. Prior to placement of any fabric – pre moisten to avoid wicking of moisture from the concrete that can result in the fabric texture negatively absorbed into the concrete surface.

Article courtesy of Cement Concrete & Aggregates Australia website - www.ccaa.com.au

Specifying Slip Resistance

General - Slip resistance is typically specified by nominating an appropriate class from those listed in AS/NZS 4586 test methods. To assist with this decision, HB 197 Table 3 gives guidance on the appropriate classes of slip resistance for a variety of applications. The relevant classification and test method for various end uses is given below.

Since the wet pendulum test will always be used for conducting slip resistance audits (and accident investigations) it is recommended that the slip resistance of polished concrete be specified in terms of the AS/NZS 4586 wet pendulum classifications.

Sloping surfaces and ramps should be given special consideration. The Building Code of Australia requires that ramps must have a nonslip finish, and limits the maximum gradient of accessible ramps for disabled access to 1 in 14. In any other case, the maximum gradient is 1 in 8. AS 1428.17 requires that the gradients and cross fails of the surface area within a landing or circulation space shall not exceed 1:40. Slopes of 1 in 100 to 1 in 40 are typically provided in surfaces, both internal and external. Surfaces with slopes of 1 in 20 (about 3°) to 1 in 8 are regarded as accessible ramps and require safety features such as handrails and tactile ground surface indicators. Some surfaces with slopes between these two ranges (i.e. 1 in 40 to 1 in 20) may warrant particular attention since they present a higher slip hazard but without having the safety features associated with ramps, e.g. handrails.

General Pedestrian Areas - These include areas such as courtyards, paths, walkways, driveways and the entrances to and circulation areas within publicly accessible buildings. When specifying polished concrete floors in general pedestrian areas, the guidance in HB 197 should be considered before specifying that the concrete have the appropriate Class V, W, X, Y or Z slip resistance in accordance with the wet pendulum test, Four S rubber Table 1. As the risk of slipping depends on many factors, the designer must consider to what extent various other design decisions will influence the overall risk of slipping when the concrete is wet (or contaminated). 

External public areas and walkways generally require a Class W slip resistance surface, in order to ensure that the floor does not make a high contribution to the risk of slipping when wet. Class W surfaces were specified for all the external case studies examined in this Data Sheet (see Achieving Slip Resistance) and is recommended in HB 197. For entrance areas and other interior situations, such as bars/taverns and food court areas, where occasional contamination may occur, HB 197 recommends Class X surfaces. This is appropriate where the risk of slipping when wet is mitigated by promptly cleaning up spills and rainwater. For interior floors such as hotel foyers, offices, supermarket aisles and other public buildings/areas that are maintained in a clean and dry condition, the risk of contamination is very low and HB 197 recommends Class Z as an appropriate level of slip resistance.

Similarly, for polished concrete floors in residential applications where any spills are generally spot cleaned immediately to maintain the surface in a dry condition, Class Z would also be appropriate. Bathrooms and other 'wet' areas would generally require a Class X slip resistance.

While the wet pendulum test classifications are suitable for surfaces that have a maximum 1 in 20 slope, HB 197 recommends that the use of Class V for external ramps (i.e. steeper than 1 in 20). HB 197 also has an appendix that details a method for calculating the slip resistance class required for ramps. The procedure is as follows:

1. Convert the required BPN value of the 'level' surface to a coefficient of friction, μ equal to 3P/(330-P), where P is the recommended BPN value for the level surface.
2. To allow for the slope, increase the value of μ by an amount equal to the slopes (expressed as a percentage) multiplied by 0.0125.
3. Convert the resulting coefficient of friction back to a BPN value equal to 330μ/ (3+μ)
4. Select the appropriate slip resistance class.

The wet pendulum test may be used within a range of ±10° from level (slope of about 1 in 5.7).When assessing whether or not a sloping surface has adequate slip resistance, use the same procedure as in the examples above, and compare] the obtained result with the required BPN . The AS/NZS 4586 wet pendulum test can be used to check the compliance of new surfaces, while the AS/NZS 4663 wet pendulum test can be used to monitor changes in the slip resistance over time. For measuring the slip resistance of slopes steeper than 10°, a flatter area either at the top or bottom of the ramp (having the same surface texture and roughness as the slope) may need to be used for the test.

An alternate approach for ramps is to specify a Class R10 for dry internal ramps, or an R11 or R12 for external ramps Table 2. However, since the oil wet ramp test can only be conducted in the laboratory, compliance can only be assessed by secondary means such as wet pendulum tests and Rz surface roughness measurements. HB 197 contains recommendations for specific locations in terms of the R9 to R13 classifications. The angles do not relate to the steepness of the ramp that can be safely traversed.

Surfaces intended specifically for barefoot use -  These should be specified as having a slip resistance Class A, B or C in accordance with AS/NZS 4586, wet/barefoot ramp test Table 3.

HB 197 contains recommendations for specific locations in terms of the A, B and C classifications. As with the oil-wet test, this test is used merely to assess the relative slip resistance of level surfaces. A higher classification may be appropriate in the case of sloping surfaces.Examples include:

Class A - Barefoot passages (mostly dry), changing and locker rooms, swimming pool floors where water depth >800 mm.
Class B - Barefoot passages not covered by Class A, shower rooms, pool surrounds, swimming pool floors where water depth <800 mm, toddlers’ paddling pools, some stairs leading into the water
Class C - Walk-through wading pools, sloping pool edges

Commercial and Industrial Applications As floors in many businesses and industrial applications can be subjected to a wide range of contaminants, their slip resistance is normally specified in accordance with the oil-wet ramp test Table 2. This test is used merely to assess the relative slip resistance of surfaces and the classifications are applicable to level surfaces. (Note: Oil-wet ramp test can only be conducted in the laboratory and compliance can only be assessed by secondary means such as the wet pendulum test). The wet pendulum test is the most appropriate means of specifying the slip resistance of concrete surfaces.

Table 5 in HB 197 gives guidance on suitable classifications for various commercial and industrial applications. HB 197 often recommends that surfaces should have a minimum displacement volume determined in accordance with AS 4568. Where it recommends a profiled surface, such as an R11 and V4 finish for car wash areas, it is best to go to a higher classification, in this case R12. Examples include:

Class R9 - Dining rooms, shops, operating theatres, hairdressing salons, classrooms.
Class R10 - Entrance areas in public buildings where moisture can enter from the outside. Social facilities (toilets, washrooms), some kitchens, most bathrooms and wash facilities, garages, and covered areas of multi-storey carparks.
Class R11 - Laundry areas, florist shops, vehicle repair workshops, aircraft hangers.
Class R12 - Most food processing/production facilities and large commercial kitchens.
Class R13 - Slaughtering, processing of meat, fish and vegetables

Article courtesy of Cement Concrete & Aggregates Australia website - www.ccaa.com.au

Part III: Achieving desired slip resistance coming soon...

Achieving the desired slip resistance 

When specifying the slip resistance of polished concrete surfaces, an optimization of appearance and required slip resistance needs to be made. For example, high gloss finishes may not achieve the required slip resistance for some applications. It is therefore important to consider the slip resistance offered by the combination of finish, texture and sealer (if present) so that the slip resistance and finish requirements can be realistically specified and achieved. The advice of a hard-flooring specialist may be sought regarding the appropriate combination of finish, texture and sealer for the slip resistance performance required.

To provide some guidance, numerous case studies have been carried out to determine what effect variations in the finish, texture and sealer have on the slip resistance. The studies highlighted the following specific points, which should be considered when specifying and constructing slip resistant concrete finishes.

• For external pavements, wet pendulum Class W finishes were consistently specified. A honed finish at 80–100 grit with a penetrating sealer applied gave satisfactory slip resistance. Honed finishes and penetrating sealers give consistent results due to the uniform texture provided.
• Concrete finishes that are honed with a finer grit provide lower slip resistance and therefore increased risk of slipping when the floor is wet.
• Honed finishes generally provide satisfactory results in accordance with the recommendations in HB 197, but may be rendered inadequate by the application of a surface coating.
• Unsealed surface. The case studies revealed BPN s typically greater than 54 where appropriately honed surfaces remained unsealed. However, increased wear over time and resultant polishing of the surface, or loss of texture-providing aggregates should be considered.
• Surface coatings or other products that form a film on the surface generally give unsatisfactory results.
• For large areas, the sealer should be applied to a sample spot and slip resistance tested prior to the application of the sealer to the entire area. This is especially true for coating type sealers as they generally provide much lower slip resistance.
• Penetrating sealers provide better results than those that form a coating or film on the surface. They also assist in maintaining slip resistance by maintaining the surface roughness.
• Rougher textures generally provide higher slip resistance results, but may be harder to clean.
• Uniform application of sealer is important as this will give consistent slip resistance results over the surface. Note that variable slip resistance is considered to be a hazard.
• Applied coating with aggregate broadcast into the coating must have the aggregate distributed uniformly to avoid variable slip resistance.
• Surface wear may decrease slip resistance by either polishing the surface or removing texture-providing aggregate from the surface. Basic concrete quality issues must therefore be addressed to ensure durability of the surface
• Polished surfaces used in foyer areas should have matting at all entries to try and remove water and dirt walked in by the public. Spot cleanup with clean mops or cloths should also be undertaken as required.
• Use of colour pigments in the concrete does not affect the slip resistance.
• Broom finishes provide greater slip resistance across the grain than along it. This finish should therefore be provided normal to the direction of pedestrian movement if possible.
• Stamped and broom finishes give similar slip resistance results as only the micro-roughness of the surface contributes to slip resistance.
• Abrasive blasted finishes can provide variable results due to uneven removal of surface mortar. They are generally suitable only for external use due to the aggressiveness of the finished surface and difficulty in maintaining these types of finishes internally.
• Finishes must suit the application. Rough finishes should be used only where constant contamination with water or other liquids/solids is present.
• Ramps may require increased roughness.

Article courtesy of Cement Concrete & Aggregates Australia website - www.ccaa.com.au

Introduction

Slip resistance of floors and pavements is a measure of the ability of a surface to resist accidental slipping by pedestrians - in dry or wet conditions. There is an expectation that surfaces will provide adequate slip resistance and this is increasingly being incorporated into regulations.

Polished concrete floors is a generic term that describes a variety of exposed decorative concrete flooring options often having a highly polished or gloss surface finish. With the increasing popularity of these types of finishes the issue of providing adequate slip resistance has become an important consideration.

This data sheet examines the factors influencing the slip resistance of a surface and methods of measuring, specifying, achieving, maintaining and improving slip resistance. It focuses on the factors related to the concrete floor or pavement surface that impact on the risk of slipping, which include the surface finish, texture and applied sealer (if present) that combine to produce a final surface roughness. A number of case studies have been examined to determine the factors contributing to whether or not the specified slip resistance was achieved.

"Slip resistance of floors and pavements is a measure of the ability of a surface to resist accidental slipping by pedestrians - in dry or wet conditions"

Factors Influencing Slip Resistance

Pedestrian slip resistance is a complex subject, where the likelihood of a slip is a function of a variety of factors such as the surface (type and texture), the environmental conditions, and the individual users (their physical condition and footwear). The reasons for accidental falls on concrete surfaces can be divided into four categories:

• External factors - These are essentially hazards such as stepping (vertical displacement) at footpath cracks and other slab joints, slippery floor surfaces and slopes. These can be minimised through good design and installation practices, good cleaning and maintenance practices safety audits, remedial policies, and mandatory legislation. Footwear may be considered an external factor, since inappropriate or excessively worn footwear may be the primary cause of an accident.
• Internal factors - These include voluntary and involuntary responses of people to environmental factors such as distractions. Responses may also be influenced by stress, fatigue, medicinal and recreational drugs, and also by the person's mood and the degree of preoccupation (which may be influenced by the nature of the activity being undertaken - carrying, pushing, rushing), and whether it imposes a temporary functional limitation, e.g. obscured vision or impaired balance. 
• Environmental factors - These include lighting conditions, contamination of the surface (by water or other materials) and slopes. The risks can be minimised by good design practices (lower gradients, less glare) and staff training (response to spills, replacement of light bulbs).
• Pathological factors - These include ageing, impaired vision, physical abilities, instantaneous health conditions (e.g. stroke, heart attack) and diseases (e.g. Parkinson's disease).

Sufficient micro-roughness is necessary to provide the fictional force or 'grip' required to prevent footwear (and bare feet) from slipping. Micro-roughness is the irregularities in a walking surface, often invisible to the naked eye, with a surface roughness (Rz) typically between 10μm and 100μm as measured by a surface roughness meter. The coarser the surface roughness, the greater will be the slip resistance, especially when contaminated by water or a range of other substances. This is dealt with in more detail in the section on improving slip resistance.

Measuring Slip Resistance

While the surface roughness can be measured, the two common methods used to assess wet slip resistance are the wet pendulum test, which measures the frictional force offered by simulating a foot moving over a water-contaminated surface, and the ramp test, which determines the maximum gradient at which a person can just traverse the surface, either barefoot (wet barefoot test) or in shoes (oil-wet test). AS/NZS 45863 also includes a friction test method for dry floors. Since most wet floors will provide adequate slip resistance when clean and dry, this test is not commonly specified.

Wet Pendulum Test - This test (AS/NZS 4586) is generally used in the laboratory for classifying the wet slip resistance of new flooring (pedestrian surface) materials. However, as the test instrument is portable Figure 1, it can also be used on site to assess the slip resistance of existing floors and pavements (AS/NZS 46634).

The instrument has a rubber slider attached to a spring-loaded foot at the end of a pendulum arm (leg). The pendulum arm is released from a horizontal position, allowing it to swing so that the slider contacts the wet pedestrian surface over a set distance of 126mm. The extent to which the pendulum fails to read its release height on the oversewing is used as a measurement of the slip resistance. The reading on the scale is the British Pendulum Number (BPN).

The AS/NZS 4568 classifications for slip resistance based on this test using a Four S (simulated standard shoe sole) rubber are given in Table 1. Note that a TRL (Transport Research Laboratory) rubber can also be used (listed in Table 2 of AS/NZS 4586) but the results are sensitive to temperature and a correction must be applied. A Four S rubber is typically specified as it is generally considered to best differentiate between the slip resistance of smoother surfaces. The TRL rubber is sometimes used when considering wet barefoot slip resistance. Figure 1

Ramp Tests - These tests use human subjects to subjectively assess the slip resistance of pedestrian surfaces under closely controlled conditions. The subjects walk forwards and backwards on a ramp (Figure 2) while the operator progressively increases the angle of inclination, until the subjects reach the 'zone of insecurity' where they either experience slipping or sense that they will fall if the angle is further increased. The angles of inclination reached are used to assess the friction characteristics of the test surface. The test is not intended to provide guidance on the angle of ramps for which a particular classification is suitable. There are two principal test methods: the wet barefoot test and the oil-wet test.

• Wet Barefoot Test - For the test procedure described above, the subjects are barefoot and water is applied to the surface being tested. This method is accepted as the best means for assessing the slip resistance of materials that are intended for use in barefoot areas, such as showers and swimming pools.
• Oil-Wet Test - This involves coating the material surface with engine lubricating oil, and having two test subjects wearing standard test shoes, walking forwards and backwards on the ramp to determine the inclination at which safe walking is no longer possible. Facing downhill and with an upright posture, each subject in turn moves backwards and forwards over the test surface as the angle of inclination is gradually increased, until the safe limit of walking is reached. Subjective influences on the acceptance are limited by means of calibration procedure. This test method is accepted as best means for assessing the slip resistance of materials that are intended for use in industrial premises, where the nature and extent of the contamination can be predicted, and staff can be compelled to wear appropriate footwear.

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Article courtesy of Cement Concrete & Aggregates Australia website - www.ccaa.com.au