The present invention relates to paving materials, and particularly to paving materials containing a bituminous binder (for example, but not limited to an emulsion) when applied, such as for roads or other paving surfaces. In particular, though not exclusively, the invention relates to cold bituminous emulsion mixtures.

The term cold bituminous emulsion mixture "CBEM" includes an extensive range of products, preparing procedures and laying techniques. This mixture may be made by mixing together open or dense-graded aggregates, virgin aggregates or Reclaimed Asphalt Pavement (RAP), and cationic or anionic bitumen emulsion which may be a normal bitumen emulsion or may be modified by addition of a polymer or solvent.

Cold bituminous emulsion mixtures may be prepared on site using special equipment or by hand mixing, using an asphalt mixture plant. The mixture may be stockpiled before final laying. The process of spreading and laying may be performed by hand, by graders or using asphalt pavers. Cold bituminous emulsion mixture is typically used as a structural layer in heavily trafficked base layers, and low trafficked wearing courses, and as a non-structural layer in surface treatment layers.

However, cold bituminous emulsion mixtures have many restrictions and therefore have been considered poorer than Hot Mix Asphalt mixtures for a number of reasons. These include that the compacted cold mixtures are high in air-void content, which reduces strength and is undesirable. They have weak early life strength (caused mainly by the trapped water), and long curing times (evaporation of water, volatiles content and setting of emulsion).

The present invention aims, desirably, to address at least some of these problems. At its most general, the invention proposed is the use of ashes in a bituminous mixture (hot, warm or cold). The ashes may be a by-product, or waste materials. Surprising benefits have been found when utilizing such ashes in bituminous (e.g. emulsion) mixtures. Firstly, an improvement in engineering properties is observed. In general, an enhancement of ultimate strength is observed due to the cementitious properties of the ashes within the mixture. Secondly, trapped liquid water may be reacted with the ash materials to complete the hydration process with the result that trapped liquid water is removed. This reduces the curing period of the bituminous (e.g. emulsion) mixture, particularly when a cold mixture.

Paving materials such as for roads or other paving surfaces, may cure more quickly and be stronger when cured.

In a first of its aspects, the invention may provide a bituminous mixture for paving including:

a first constituent material comprising a bituminous binder; and

a second constituent material comprising an ash containing by % weight of the ash: from 20% to 80% CaO; from 10% to 60% Si0 ₂ ; from 1 % to 10% Al ₂ 0 ₃ ; from 1 % to 10% MgO.

For example, the bituminous binder may be a bituminous emulsion, or foamed asphalt binder, or warm asphalt binder.

The bituminous binder may comprise an asphaltene. The asphaltene may be defined by the chemical formula CTSHSI NLOSU 0 _{2 2} (e.g. ASP-H), or Cei Hsi NkoSzo O _{2 0} (e.g. ASP-M), or C51 H55NL0S1.0 O1.0 (e.g. ASP-D). The bituminous emulsion may be a water-based emulsion. Foamed asphalt may be prepared by heating asphalt to reduce viscosity and subject it to high pressure water to produce a foam. Warm asphalt binder may be prepared by adding an additive(s) which serve to reduce the temperature at which the viscosity becomes suitable for mixing with aggregate.

Preferably, the bituminous binder may be, or may include, a bituminous emulsion mixture such as a cold bituminous mixture (CBEM). The mixture may be made by mixing together open or dense-graded aggregates, virgin aggregates or Reclaimed Asphalt Pavement (RAP), and cationic or anionic bitumen emulsion which may be a normal bitumen emulsion or may be modified by addition of a polymer or solvent.

The second constituent material may comprising an ash containing by % weight of the ash: from 45% to 75% CaO; from 15% to 45% Si0 ₂ ; from 1 % to 10% Al ₂ 0 ₃ ; from 1 % to 10% MgO. The ash may contain from 0.1 % to 10% of iron, such as Fe ₂ 0 ₃ , by % weight of the ash. Other forms of iron than Fe ₂ 0 ₃ may be present in this.

The ash may contain, by % weight of the ash, from 45% to 75%, or preferably from 50% to 70% CaO, or more preferably from 50% to 65% CaO, or yet more preferably, from 50% to 60% CaO.

The ash may contain, by % weight of the ash, from 15% to 45%, or preferably from 20% to 40% Si0 ₂ , or more preferably from 20% to 35% Si0 ₂ . The ash may contain, by % weight of the ash, from 1 % to 5% Al ₂ 0 ₃ , or more preferably from 2% to 5% Al ₂ 0 ₃ .

The ash may contain, by % weight of the ash, from 2% to 6% MgO. The mixture may comprise a third constituent material comprising silica (Si0 ₂ ) particles with an average diameter of less than 75 microns. The third constituent material comprising silica (Si0 ₂ ) particles composed of at least 75% silica. The average diameter may be less than 10 microns, or more preferably less than 5 microns, such as 2 microns or less, or most preferably less than about 1 micron. The surface area of the particles (e.g. as determined by BET analysis, the well-known Brunauer, Emmett and Teller method for determining specific surface area) may be between 13,000 and 30,000 m ² /kg. Preferably, the Silica particles are composed of at least 90% Silica, or preferably at least 95% Silica (e.g. at least 98% Silica). The composition preferably comprises a blend of the first and second constituent materials provided separately and blended together.

The third constituent material may comprise silica fume (SF). Silica fume is also known commercially as microsilica, condensed silica fume, silica dust or volatilized silica, and it may be provided as a by-product of producing silicon metal or ferrosilicon alloys. Silica fume consists primarily of amorphous (non-crystalline) silicon dioxide (Si0 ₂ ). The individual particles are extremely small. Because of its fine particles, large surface area and the high Si0 ₂ content, Silica fume has been found to be a very reactive pozzolan. The Si0 ₂ content of Silica fume may range from 85%, 88%, 90%, 92%, 94%, 96% or 97.5%. Silica fume may be defined according to the ASTM C 1240 Standard Specification for silica fume, though this is by no means exhaustive or exclusive in the present invention. The silica of the third constituent material may comprise particles with an average diameter of less than 50 microns. The particles may comprise agglomerates of smaller particles of silica. The smaller particles of silica may have an average diameter of less than 5 microns. The smaller particles of silica may be agglomerates of yet smaller particles of silica which may have an average diameter of preferably less than a few microns (e.g. 1 micron or less).

The mixture may comprise a fourth constituent material comprising an aggregate. The aggregate particles may be of organic or non-organic nature with an average diameter of 0.001 microns to 75mm.

About eleven million tonnes of paper sludge waste are produced annually in Europe. For example, a newsprint mill may produce new paper form recycled paper in a process which creates unusable waste called "paper sludge" containing cellulose fibres. This waste paper sludge is typically incinerated to generate energy for use in the same industry. The fly ash resulting from the incineration of waste paper sludge is very white coloured and its alkalinity is typically very high. It is generally known as paper sludge ash.

The second constituent material may comprise paper sludge ash (PSA). It has been found that calcinations of paper sludge occur by incineration of the sludge at a temperature of about 700°C for about 2 hours. This has been found to convert kaolinite within the incinerating sludge in to reactive amorphous metakaolinite. This increases the pozzolanicity of the paper sludge ash. Preferably, the paper sludge ash of the first constituent material is prepared accordingly.

The paper sludge ash may be in the form of a fly ash. The term "fly ash" includes a reference to a fine particulate ash typically sent up by the combustion of fuel, such as a solid fuel, and discharged as an airborne emission or recovered or captured as a byproduct. Examples of the properties of some fly ashes include those defined according to European Standard BS EN 450. Preferably, the alkalinity of the paper sludge ash is high or very high.

The main chemical components of paper sludge ash preferably include: calcium oxide, silicon oxide, aluminium oxide and magnesium oxide. The main mineralogical components preferably include one, some or all of: gehlinite, calcite, lime and anorthite.

Paper sludge ash (PSA), can be generated from burning paper waste. One example is a boiler ash residue resulting from the incineration of paper sludge in energy production. Annually 125,000 tonnes of PSA is generated in the UK by paper mills. The main ingredients of PSA are Si0 ₂ , and CaO. It has been found that a pozzolanic reaction can be generated when PSA is mixed with a cold mixture component. Furthermore, the water absorptive ability of PSA has been found to be high and to be surprisingly useful for absorbing trapped water in CBEMs.

The present invention relates to use of waste paper sludge ash, with or without other different wastes such as steel slag products, or silica fume, also known commercially as microsilica, (in powder or slurry forms), to improve a cold bituminous (e.g. emulsion) mixtures' compactability, strength and durability for use in construction. Preferably the PSA is a fly ash. These waste materials have been found to chemically react with traditionally cold mixture components, to improve the final cold mix product. The final product is suitable, for example, for use in producing a surface such as a street surface, base layers for streets, highways, airfields and other roads and walkways, pavements and or other civil engineering construction applications.

Waste or by-product material such as paper sludge ash, with or without other waste materials and/or (silica fume/microsilica) may be employed. The present invention may provide a cold bituminous mixture (e.g. comprising foamed asphaltic binders or emulsion mixtures (e.g. CBEMs)) using waste paper sludge ash and, optionally, with other waste materials with or without silica fume (microsilica) for use in the production of a road, airfield or other civil construction.

According to the present invention a process of preparing cold bituminous mixtures using waste paper sludge ash, optionally with other waste materials, and optionally with silica fume is provided. The process may principally comprise replacement of the mineral filler of traditional bituminous mixtures (e.g. Cold Bituminous Emulsion Mixture) with the second constituent material defined above (e.g. PSA). Other materials may be added as extra additives. PSA may be added in conjunction with other fillers. The other fillers may be mineral, organic or inorganic such as fine fibres, rubber, plastic or polymer powders or slurry, or limestone dust or rock dust.

The second constituent material (e.g. waste PSA) is preferably ground to fine powder before being incorporated to the mix in order to increase its particle surface area. The chemical reactivity of the ground material has been found to be increased by the grinding. However, it can be used without grinding. According to the present invention, bituminous mixtures (e.g. CBEMs) may comprise waste PSA as a replacement of mineral filler in the replacement percentage of 25% to 100%. Such mixtures have shown a significant improvement in terms of mechanical properties and durability. However, adding other waste materials to PSA individually or collectively such as steel slag (SS), granulated ground blast furnace slag (GGBFS), pulverised fuel ash (PFA), biomass fly ash (BFA), Ely ash, the ford bag fly ash, andsStraw ash (ground or un-ground) and with level of 1 % to 25%, or more preferably 1 % to 5.5% of the total aggregate mix by %wt also shows some improvement in the mixture. Additionally, silica fume (in slurry or powder forms) with a level of zero% to 4%, by % of total aggregate weight, in the mix has shown a significant improvement in the mechanical properties and durability of bituminous mixtures (e.g. CBEMs). Preferably, the ashes are fly ashes.

The aggregate may be of any type normally used in paving or road engineering such as granite, limestone, steel slag, basalt or the like.

According to the present invention, there are two process which are believed to happen when the second constituent material (e.g. PSA) is incorporated in the bituminous mixture. Firstly, the high absorb ability of the second constituent material (an ash, such as PSA) will reduce the trapped water between the aggregate surfaces and the bitumen residue. Secondly, a hydration process is initiated as the ash (e.g. PSA) has pozzolanic properties which develop a cemintitous composition in the presence of water. The cemintitious product and the absence of the previously trapped water accelerate and improve the strength of the bituminous mixture. The aforesaid other waste materials and silica fume have also been found to accelerate the chemical reactivity of the second constituent material (e.g. PSA) and the hydration process within the mix. These materials and reactions tend to result in chemical reactions which form cementitious products, namely calcium aluminate hydrates, calcium-almino silicate hydrates, calcium silicate hydrates, calcium alumina- sulphates, etc.

A cold bituminous (e.g. emulsion) mixture may be provided in this way for use in low, medium and heavy trafficked flexible pavement constructions. It may comprise an aggregate comprising a course aggregate and/or a fine aggregate and/or a filler, a bitumen binder (e.g. emulsion), and a further material wherein the course aggregates may comprise crushed aggregates (e.g. green granite), and the fine aggregates may comprise crushed aggregates (e.g. green granite or steel slag). The filler may comprise, for example, crushed aggregate dust. The bitumen binder may comprise standard bitumen emulsion and or polymer based emulsions, or equivalent, or a foamed asphalt or a warm asphalt binder.

The aforementioned further material may comprise the ash of the second constituent material, such as paper sludge ash. The further material may further comprise any one or more of steel slag (SS), granulated ground blast furnace slag (GGBFS), pulverised fuel ash (PFA), biomass fly ash, Ely Ash, The ford bag fly ash, and straw ash. The cold bituminous emulsion mixture may further comprise an additive comprising silica fume. The percentage proportion of the second constituent material (e.g. paper sludge ash) may be at least 0.25% or optionally at least 1.0% of the total aggregate content (e.g. by % weight). The percentage proportion of the second constituent material may range from 0.1 % to 5.5% of the total aggregate content. The silica fume content may range from 0.0% to 4 % of the total aggregate content.

The invention may provide a method of preparing the cold bituminous (e.g. emulsion) mixture as described above comprising the mixing of the aggregate including the ash, with pre-wetting water and then adding the bitumen mixture. The second constituent material (e.g. paper sludge ash) may then generate a cementitious reaction with the cold bituminous emulsion mixture component. The mixing of the aggregate with pre-wetting water may then be followed by adding the bitumen mixture (e.g. emulsion).

The second constituent material (e.g. paper sludge ash) optionally with other further materials, may generate a cementitious reaction with the cold bituminous mixture component.

The method may comprise mixing into the aggregate any added silica fume with pre- wetting water in a proportion of silica fume ranging from 0% to 28% of the total aggregate content (e.g. by % weight), and then adding the bitumen mixture (e.g. emulsion). The second constituent material (e.g. paper sludge ash) may generate a cementitious reaction when mixed with the cold bituminous mixture component. The micro-silica may serve as an activator of/for the second constituent material and increase the mechanical properties (e.g. strength when cured, reduced porosity to water etc.) of the mix.

The invention may provide a product comprising a surface layer, road base layer (e.g. suitable for low, medium and heavy traffic roads), a highway or airfield paved using the cold bituminous (e.g. emulsion) mixture.

The products may desirably be cured and open to traffic in less than 3 days. The paper sludge ash particle size/fineness second constituent material (e.g. paper sludge ash) has been found to effect the improvements provided by the invention. The more the particle fineness the more is the increase in the improvement of the strength and durability properties of the cured product. Preferably, the ash particle sizes range from 1 μηι to Ι ΟΟμηι, or preferably 5μηι to 60μη-ι.

The invention in a further aspect provides the use of the mixture to produce the product. A yet further aspect comprises the use of the product. The product may be formed after mixing at roadside, on a construction site or on/in a mixing plant. The use of the product includes engineering construction projects such as pavements, roads, yards, car parks, school playgrounds, tennis yards, channel lining etc.

The invention preferably provides hot, medium and cold bituminous mixtures containing ashes (e.g. especially paper sludge ash) as additives or filler materials to improve the mechanical properties of the products for use in paving construction. Use of paper sludge ash (PSA) in the mixture may be with or without any one, some or all of the following further materials: steel slag (SS), granulated ground blast furnace slag (GGBFS), pulverised fuel ash (PFA), biomass fly ash, Ely Ash, ground or unground. The ford bag fly ash, straw ash ground or non-ground and silica fume (in slurry or powder forms) to improve the mechanical properties and durability of cold bituminous emulsion mixtures. Within the cold mix preparation process, the further material(s) chemically react with the other traditionall cold mixture components to produce new materials. A multi-stage mixing technique may comprise traditional techniques which include pre-wetting the aggregate then adding a bituminous emulsion. Alternatively, according to preferred aspects of the invention, the second constituent material may be wetted together with the aggregate then the bituminous binder may be added to the mixture of the aggregate and the second constituent material. Alternatively the aggregate may be wetted, the bitumen may then be added and the second constituent then added. The second constituent material may be added together with one or more "further materials" and/or the silica fume.

Preferably the entire mixing process is to be preformed within 3 minutes.

The invention may provide a method of preparing a bituminous mixture comprising: providing a first constituent material comprising a bituminous binder; providing a second constituent material comprising an ash containing by % weight of the first ash: from 20% to 80% CaO; from 10% to 60% Si0 ₂ ; from 1 % to 10% Al ₂ 0 ₃ ; from 1 % to 10% MgO; providing an aggregate; and pre-wetting the aggregate with water; and adding the second constituent material to the aggregate; and adding the bituminous binder to the aggregate; wherein the adding of the second constituent material is performed before or after the pre-wetting of the aggregate is performed; and, the adding of the bituminous binder is performed before or after the adding of the second constituent material is performed. The second constituent material may be as described above. The adding of the second constituent material may be performed before the pre-wetting of the aggregate is performed; and, the adding of the bituminous binder may performed before the adding of the second constituent material is performed. The adding of the second constituent material may be performed before the pre- wetting of the aggregate is performed; and, the adding of the bituminous binder may performed after the adding of the second constituent material is performed. The adding of the second constituent material may be performed after the pre-wetting of the aggregate is performed; and, the adding of the bituminous binder may performed before the adding of the second constituent material is performed. The adding of the second constituent material may be performed after the pre-wetting of the aggregate is performed; and, the adding of the bituminous binder may performed after the adding of the second constituent material is performed.

The second constituent material (e.g. paper sludge ash) may be used as at least a partial replacement of the traditional mineral filler portion in the bituminous mixture, with the replacement percentage range from 5% to 100% or preferably 25% to 100%. However, the further material(s) listed above may be used as extra material to the mix to increase the chemical and physical activity of the second constituent material within the mix. Silica fume can be used also as an activator of the paper sludge ash with a content level ranging from 0% to 4% of the weight of aggregate in the mix.

Paper sludge ash has beneficial pozzolanic reactivity characteristics which generate cementitous/binding properties within the bitumen (e.g. emulsion) mixture, where its water and or liquid absorptive ability reduces the quantity trapped water and/or liquid within the mixture. This improves the early- and long-term strength of the mixture when cured, and its mechanical and durability properties improve rapidly. The silica fume and the slag (SS, GGBFS & PFA) materials collectively or individually play the role of activating the second constituent material within the mix.

Non-limiting embodiments of the invention shall now be described in order to illustrate the invention with reference to the accompanying drawings.

Figure 1 illustrates aggregate particle size grading;

Figure 2 illustrates the effects of different proportions of PSA on the resulting strength of a cured sample, according to a first two-stage curing regime;

Figure 3 illustrates the effects of different proportions of PSA on the resulting strength of a cured sample, according to a second two-stage curing regime; Figure 4 illustrates the effects of different proportions of PSA on the resulting strength of a cured sample, according to a third two-stage curing regime;

Figure 5 illustrates a comparison of predicted strength values in samples versus measured strength values, the prediction being made according to a statistical model;

Figure 6 illustrates measured values of accumulative creep strain in samples;

Figure 7 illustrates the effects upon creep stiffness of different % PSA contents in samples;

Figure 8 illustrates the effects upon creep rate of different % PSA contents in samples. In the drawings, like items are assigned like reference symbols.

The embodiments described below concern the use of paper sludge ash (PSA) as the second constituent material defined above, as a filler in a cold bitumen emulsion mixture to overcome the problem of inferiority of cold mixes, namely low tensile stiffness and creep stiffness. Paper sludge ash (PSA) which is used in the following embodiments is boiler ash residue resulting from incineration of paper sludge in energy production. The main ingredients of PSA are Si0 ₂ and Al ₂ 0 ₃ .

Therefore, a pozzolanic reaction may be generated when mixed with cold mixture components. On the other hand, the water absorptive ability of PSA is high, and PSA has been found useful for absorbing trapped water in CBEMs.

The CBEMs presently employed used PSA in the proportion from 0% to 5.5% of the aggregate weight. The improvements in mechanical properties were determined using the indirect tensile stiffness modulus and unaxial compressive cyclic test. These are respected indicators of the mechanical properties. A statistical model is also built to identify the change in stiffness modulus due to parameters, namely, filler percentage, and curing time. 1. Materials and sample preparation method.

1 .1 Materials

The aggregate used in the present embodiments is crushed green granite from Cliffe Hill quarry and the aggregate gradation is given in Table 1. The physical properties of the aggregates are given in Table 2. The aggregate were dried, riffled and bagged with sieve analysis achieved in according with standards BS EN 933-1 and BS EN 12697-28. In order to ensure appropriate interlocking of the close graded surface course, mix gradation was selected according to standard BS EN 4987-1 : 0/10 mm close graded surface course gradation has been used in the following embodiments. The grading of 0/10 mm mix is shown in Figure 1 .

Test sieve aperture size % by mass passing % by mass passing mm specification range mid

14 100 100

10 95-100 97.5

6.3 55-75 65

2 19-37 28

1 10-30 20

0.063 3-8 5.5

Table (1): Aggregate grading for 0/10 mm size close graded surface

course BS EN 4987-1 .

Property Value

Coarse aggregate

Bulk specific gravity, gm/cm ³ 2.79

Apparent specific gravity, gm/cm ³ 2.82

Water absorption % 0.4

Fine aggregate

Bulk specific gravity, gm/cm ³ 2.74

Apparent specific gravity, gm/cm ³ 2.77

Water absorption % 0.4

Table (2): Physical properties aggregates. The selection of this gradation is due firstly to this gradation having been used successfully in the heavy traffic surface coarse hot coated macadam (BS EN 4987:1 , 2005). Secondly, the dense gradation has a greater proportion of coarse aggregates as compared with close gradation. The more coarse aggregate grading results in insufficient compactability and specimens tended disintegrated upon extrusion.

Cationic bitumen emulsion was selected to ensure high adhesion between aggregates particles. Cationic slow setting emulsion (K3) was used in the present embodiments. Table 3 show the properties of the selected emulsion, whereas Table 4 shows the chemical composition of the paper sludge ash used in these embodiments.

Property Value

Appearance Black to dark brown liquid

Boiling Point (° C) 100

PH 5

Relative Density at 15 ⁰ C gm/ml 1 .05

Residue by distillation, % 56

Table (3): Bitumen Emulsion Properties (K3)

Element Concentration (%)

CaO 57.5

Si0 ₂ 28.1

Al ₂ 0 ₃ 3.62

MaO 3.73

Fe ₂ 0 ₃ 0.2

S0 ₃ 0.35

K ₂ 0 0.089

Ti0 ₂ 0.53

Table (4): chemical composition of PSA 1 .2 Sample preparation

All samples produced in the present embodiments were prepared according the method adopted by the Asphalt institute (Marshall Method for Emulsified Asphalt Aggregate Cold Mixture Design) (MS-14, 1989). The coating ability of the bitumen emulsion to the aggregates is highly sensitive to the pre-wetting water content, especially when the aggregate gradation contains a high percentage of materials passing a 63μηι sieve aperture size. Inadequate pre-wetting water content were found typically to result in balling of the binder with the fines portion of the aggregate and thus unsatisfactory coating. Different pre-wetting water contents were investigated to find the lowest percentage to ensure adequate coating. Furthermore, indirect tensile strength test were used to determine the optimum emulsion content. A mix density test was used to determine the optimum total liquid content at compaction (i.e. emulsion plus pre-wetting water contents which give highest mix density). According to the selected material characteristics, the pre-wetting water content was observed to be 4%, the optimum bitumen emulsion was 1 1 .5% and optimum total liquid content at compaction was 14.5%.

Specimens of cold bitumen emulsion mixtures were prepared using different ratios of Paper Sludge Ash (0% to 5.5%) as a replacement of mineral filler. Impact compacting (using a Marshall Hammer) was applied with 50 blows to each face of the specimens.

Moreover, conventional hot mixture samples was prepared with the same aggregate type and gradation, and 5.3% binder content was used to match the BS EN 4987 (2005) standard (0/10 mm size close graded surface course- being the preferred mixture).

Two hot mixes (made from a binder of 40/60 penetration [hard bitumen] or 100/150 penetration [soft bitumen] according to standard bituminous binder penetration test as well known to skilled person) and a cold mix were prepared in quantity to produce three 1 100 gm specimens for each specific mix. The cold mix specimens were mixed and compacted at ambient laboratory temperature (20°C to 25°C), while hot mix specimens were compacted at higher temperatures (135°C to 140°C). 1 .3 Sample conditioning

In fact, the Cold mixtures display an evolving nature, wherein the mixtures' strength characteristics are very sensitive to curing time and temperature. Therefore, samples conditioning for indirect tensile test were achieved at two stages.

Stage one was performed at a temperature of 20°C for 24 hours. A sample was left in mould before being extruded, to prevent specimen disintegration. Stage two conditioning was achieved using one of three curing temperatures, namely: 20°C; 40°C; and 60°C, each for 24 hours. In each case, the samples were tested at ages of 2, 7, 14, 28, 90 and 180 days.

The second stage curing for 24 hours at 20°C, or at 40°C, or at 60°C curing temperatures were adopted to identify the evolution of the stiffness modulus with different curing times and temperatures.

For the unaxial compressive cyclic test, the curing conditioning was selected as follows. The specimens were left in the moulds for 24 hour at room temperature before being extruded. Then the specimens placed in an oven for 14 days at 40 °C to make sure a full curing condition was attained.

2. Testing and results

2.1 Indirect Tensile Stiffness Modulus The Indirect Tensile Stiffness Modulus (ITSM) is a non- destructive test used mainly to evaluate the stiffness modus of hot mixes. ITSM at 20 °C was used to evaluate the effect of the PSA on stiffness modulus. The test was conducted in accordance with standard BS EN 12697-26:2004, a Cooper Research Technology HYD 25 testing apparatus was used. The test conditions are tabulated in Table 5.

2.2 Unaxial compressive cyclic test

The unaxial compressive cyclic test (UCCT) is a destructive test used mainly to evaluate the permanent deformation characteristics of hot mixes. UCCT at 40 °C was used to evaluate the effect of the PSA on creep stiffness. The test was conducted in accordance with standard BS EN 12697-25:2005, a Cooper Research Technology HYD 25 testing apparatus was used. The test conditions are tabulated in Table 6.

Item Range

Specimen diameter mm 100±3

Rise time 124±4 ms

Transient peak horizontal deformation 5 μηη

Loading time 3-300 s

Poisson's ratio 0.35

No. Of conditioning plus 10

No. of test plus 5

Test temperature °C 20 ±0.5

Specimen thickness mm 63±3

compaction Marshall 50x2

Specimen temp, conditioning 4hr before testing

Table (5): ITSM Test Conditions.

Item Range

Frequency 0.5 Hz

Loads 100±2 KPa

Loading pulse 1 ±0,05 s

Rest period 1 ±0,05 s

preloading 10 KPa for 10 min

Poisson's ratio 0.35 for 20 °C test tern.

No. of test plus 3600

Test temperature °C 40 ±0.5

Specimen diameter 148±5

Specimen thickness 60±2 mm

Table (6): UCCT Conditions. 2.3 Results and Discussion

2.3.1 Indirect Tensile Stiffness Modulus All cold bitumen emulsion mixture specimens for ITSM test were tested at an age of 2,7,14, 28, 90 and 180 days. The first curing time was 24 hours at a temperature of 20°C, then for 24 hours curing at one of three different curing temperatures, namely: 20°C, 40°C, and 60 °C, in order to identify the effect of PSA on the mixtures' hydration mechanism and thus on the improvement in ITSM strength. The results of these tests are shown in figures 2 to 4.

Results of ITSM tests shown in Figure 2 indicate that the stiffness modulus of CBEMs increased dramatically with the increased percentage of the PSA, and reached its ultimate values when all of the traditional mineral filler is replaced with PSA. Additionally, the ITSM were increased significantly with time, at the same time the hot mix asphalt (HMA) shows unnoticeable changes in ITSM with time. With no or low PSA percentage, no results after two days are shown in figure 2 as the specimens could not withstand the testing load. An outstanding gain in ITSM values were experienced at the other curing methods (i.e. stage two with curing temperatures of 40°C and 60 °C) with the increase in curing time and PSA percentage. Furthermore, the results show a significant increase in the ITSM for a given curing time but with increasing curing temperatures. 2.3.2 Statistical model

Using the data collected from the experimental work a statistical model was derived to predict ITSM from PSA percentage (PSA), Curing temperature (T), and curing time (CT). The unknown target model ITSM=f(PSA,T,CT) was determined as a second order polynomial function. This model can predict the variation in ITSM due to variation in PSA %, curing temperature, and curing time with a degree of significance of 0.05 (i.e. R ² =0.98). Table (6) shows the analysis of variance results, whereas the sum of the residuals is less than the sum of regression, and that is another indication of the validity of the proposed model. ITSM = c ₀ + (PSA) + c ₂ (T) + c ₃ (CT) + c ₄ (PSA) ² + c ₅ (T) ² + c ₆ (CT) ² + c ₇ (PSA x T) + c, (PSA x CT) + c _g (T x CT)

Where:

Co= -1012.805

_C1 = -494.433

c ₂ = 41.249

c ₃ = 81.399

c ₄ = 96.337

c ₅ = -0.339

c ₆ = -1 .502

c ₇ = 9.480

c ₈ = 1 1.816

c ₉ = -0.741

Where:

ITSM= Indirect Tensile Stiffness Modulus (MPa)

PSA= Paper Sludge Ash percentage (%)

T= Curing Temperature (°C)

CT=Curing Time (days)

Furthermore, Figure (5) shows the ITSM observed values plotted against the predicted values. By examining this plot, it can be seen that the predicted values are in close agreement with those observed. The plot confirms the second order polynomial model assumption, mentioned previously.

ANOVA ³

Dependent variable: ITSM

a. R squared = 1 - (Residual Sum of Squares) /

(Corrected Sum of Squares) = .980.

Table (6): proposed model parameter 2.3.3 Unaxial compressive cyclic test

The results of the unaxial compressive cyclic tests are given in figsures 6-8. Figure 6 present the accumulated strain versus pulse counts, where Figure 7 illustrates the creep stiffness of mixtures with different PSA content. Finally, figure 8 shows the creep rate of these mixtures. These figures show the general trend of the five different PSA content. The figures demonstrate the positive effect of PSA on the creep properties of CBEMs; specimens with higher PSA content had considerably longer life under cyclic load creep tests when compared to control specimens as well as with Hot Asphalt Mixtures. However, before the end of the unaxial compressive cyclic test, the control specimens gain a total collapse, while all specimens with different PSA contents withstand the 3600 pulses. This reflects that the PSA modified specimens would show a longer life than the control specimens.

The specimen with 5.5 % PSA had creep stiffness approximately 26 times bigger than the control specimens under the same testing conditions Figure 7; additionally, the same specimen had creep stiffness approximately 9 and 6 times bigger than 100-150 pen, and 40-50 pen hot asphalt mixtures respectively. This is a significant modification viewing the positive effect of PSA in CBEMs. At the same time, the creep rate of the PSA modified specimens drop to 154 times when compared the control specimen with specimen have 5.5% PSA, Figure 8.

Regarding the final conditions of control and PSA modified specimens, the control specimens showed a total collapse, whereas the 5.5% PSA specimen does not show any sign of collapse. However, specimen with 2.5% PSA showed partial signs of collapse, where hot mix shown a mark of the upper loading plate.

3. Conclusion

The embodiments have focused on studying the effect of the paper sludge ash (PSA) on improving the engineering properties of close graded surface course cold bitumen emulsion mixtures (CBEMs) in terms of stiffness modulus and creep stiffness. The invention encompasses other ashes for this purpose.

The test results confirmed that there is a significant improvement in the stiffness modulus with use of PSA, especially when 50% and more of the mineral filler is replaced with PSA. More than 9 times the value of the traditional cold mix (non-treated mixtures) stiffness was achieved when all the mineral filler (i.e.5.5%) was replaced with PSA. Furthermore, the result showed that cold mix stiffness modulus achieved is more than the HMA (Hot mix asphalt: black columns of figures 2 to 4) after 14 days of curing at 20°C curing. On the other hand, it was clearly shown that the curing temperatures played a considerable influence on stiffness modulus values. The improvements in stiffness modulus due to the use of PSA were due to two valuable PSA's characteristics. Firstly, the high water absorptive ability of PSA was shown during the mixture preparation process especially in mixing. This property did not affect the coating of the aggregates with emulsion. Secondly, the PSA has a cementitous property clearly shown through the increment in the stiffness modulus with time of curing at all curing temperature.

The test results indicate that there may be a significant improvement in the permanent resistance of mixture comprising PSA, More than a 26-fold improvement was achieved in the creep stiffness using a mixture content of 5.5% PSA. It is to be understood that the illustrative embodiments are described above are not intended t be limiting and that variations, modifications and equivalents thereto, such as would be readily apparent to the skilled person are encompassed by the scope of the invention as defined e.g. by the claims.