TECHNICAL FIELD

A concrete pavement panel that is arranged to form part of a surface of a roadway, and a method for forming such a panel is disclosed. A method for constructing a roadway comprising concrete pavement panels is also disclosed. The panel and methods may be employed in applications such as roadways on mine sites and the disclosure is herein described in that context. However, it is to be appreciated that the disclosure is not limited to that use and may be used in applications such as the construction and repair of freeways, roads, aircraft runways, railways and within industrial areas.

BACKGROUND ART

High strength and abrasion resistant road surfaces are required in many applications, such as roadways around mine sites that are subject to intensive vehicle activity. Concrete pavements are prone to a number of deficiencies that lead to rapid deterioration, especially when implemented in highly abrasive applications.

Abrasion of the pavement surface is an important mode of failure in concrete pavements subject to severe abrasion. The cause of this abrasion is a combination of loose debris present on the surface, water and heavy rubber-wheeled traffic that grinds the debris into the surface of the slab. Often, the abrasive agents cannot be avoided, so the slab must be made more resistant to the abrasion.

US 6,080,234 (Clavaud) and US 6,887,309 (Casanova) disclose an attempted solution to produce an ultra-high performance concrete (UHPC) that is highly impact resistant. The UHPC of Clavaud and Casanova incorporate fibres as reinforcement to provide post-cracking performance. However, the UHPC panels of Clavaud and Casanova are not highly abrasion resistant. As such, their UHPC panels are not suitable for applications that require high abrasion resistance, such as roadways around mine sites.

The above references to the background art do not constitute an admission that the art forms a part of the common general knowledge of a person of ordinary skill in the art. The above references are also not intended to limit the application of the apparatus as disclosed herein. SUMMARY OF THE DISCLOSURE

Disclosed herein is a concrete pavement panel having a wear surface that may be arranged to form part of a surface of a roadway. The panel may have a compressive strength of greater than or equal to 120 MPa and includes coarse and fine aggregate. The quantity of coarse aggregate may be greater than lOOOkg/m ³ and may be unevenly distributed through the panel with a higher proportion of the coarse aggregate being in the region of the wear surface. The high proportion of the coarse aggregate at the wear surface produces a highly abrasion resistant pavement surface.

Also disclosed herein is a method of forming a concrete pavement panel having a wear surface that is arranged to form part of a surface of a pavement. The concrete pavement panel may have a compressive strength of greater than or equal to 120 MPa. The method may comprise the steps of providing a suitable cementitious mixture containing at least 1000kg/m ³ of coarse aggregate, casting the mixture to produce a panel form and providing conditions to allow hardening of the mixture; wherein prior to hardening the coarse aggregate is caused to unevenly distribute in the mixture such that a higher proportion of the coarse aggregate arises in the region of the wear surface. The higher proportion of coarse aggregate at the wear surface produces a highly abrasion resistant concrete pavement panel.

Also disclosed herein is a method for constructing a roadway. The method comprises the steps of providing concrete pavement panels with an abrasion resistant wear surface and installing the concrete pavement panels such that the wear surface forms part of a roadway surface.

BRIEF DESCRIPTION OF THE DRAWINGS

Notwithstanding any other forms which may fall within the scope of the disclosure as set forth in the Summary, further embodiments of the disclosure will now be provided in the following description, which is given by way of example only and with reference to the accompanying drawings in which:

Figure 1 shows a cross section of a concrete pavement panel with a wear surface arranged to form part of a surface of a roadway;

Figure 2 shows the method steps involved in the construction of a concrete pavement panel;

Figure 3 shows a cross section of the concrete pavement panel installed as part of a roadway including levelling shims; Figure 4 shows another cross section of the concrete pavement panel installed as part of a roadway including levelling rails; and

Figure 5 shows the method steps involved in the construction of a road from multiple concrete pavement panels;

Figure 6 shows a concrete pavement panel installed above the sub-grade; and

Figure 7 shows a concrete pavement panel being cast.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

In the following detailed description, reference is made to accompanying drawings which form a part of the detailed description. The illustrative embodiments described in the detailed description, depicted in the drawings and defined in the claims, are not intended to be limiting. Other embodiments may be utilized and other changes may be made without departing from the spirit or scope of the subject matter presented. It will be readily understood that the aspects of the present disclosure, as generally described herein and illustrated in the drawings can be arranged, substituted, combined, separated and designed in a wide variety of different configurations, all of which are contemplated in this disclosure.

Failure in pavements is often caused by abrasion to the wearing surface. A major cause of abrasive damage to the wear surface of concrete pavements is heavy vehicle activity which grinds rocks and dirt into the surface of the slab. In applications just as pavements on mine sites, it is not practical to clean the debris off the pavement surface often enough to reduce or eliminate such abrasion. Rather, to reduce the effect of abrasion, a roadway surface must be manufactured and installed so that it is highly resistant to abrasion.

Disclosed herein is a concrete pavement panel having a wear surface that may be arranged to form part of a surface of a roadway. The panel may have a compressive strength of greater than or equal to 120 MPa and includes coarse and fine aggregate. The quantity of coarse aggregate may be greater than lOOOkg/m ³ and may be unevenly distributed through the panel with a higher proportion of the coarse aggregate being in the region of the wear surface. The high, or relatively increased, proportion of the coarse aggregate at the wear surface produces a highly abrasion resistant roadway surface.

In some forms, the coarse aggregate has a maximum nominal diameter of greater than or equal to 20mm. In at least one embodiment, the coarse aggregate has a maximum nominal diameter of 20-40mm. In some forms, the panel comprises between 1000kg/m ³ - 2000kg/m ³ of the coarse aggregate.

In some forms, the coarse aggregate is segregated from the fine aggregate within the panel with a higher portion of the fine aggregate being in a region of the panel spaced from the wear surface.

In at least one embodiment, the coarse aggregate is caused to have a higher proportion in the region of the wear surface as a result of settling of the coarse aggregate during forming of the panel.

In some forms, the panel is provided as a pre-cast panel. In some forms, the compressive strength of the panel is 120-160 MPa.

Also disclosed herein is a method of forming a concrete pavement panel having a wear surface that is arranged to form part of a surface of a roadway. The concrete pavement panel may have a compressive strength of greater than or equal to 120 MPa. The method may comprise the steps of providing a suitable cementitious mixture containing at least 1000kg/m ³ of coarse aggregate, casting the mixture to produce a panel form and providing conditions to allow hardening of the mixture; wherein prior to hardening the coarse aggregate is caused to unevenly distribute in the mixture such that a higher proportion of the coarse aggregate is in the region of the wear surface. The high proportion of coarse aggregate at the wear surface produces a highly abrasion resistant concrete pavement panel. In some forms, the coarse aggregate is caused to unevenly distribute in the mixture by settling as a result of possessing higher density than the paste.

In some forms, the pre-cast panel is turned over such that a lower surface of the cast panel is the wear surface when installed as part of a surface of a roadway.

Also disclosed herein is a method for constructing a roadway. The method comprises the steps of providing concrete pavement panels with an abrasion resistant wear surface and installing the concrete pavement panels such that the wear surface forms part of a road surface. The panel to be installed as part of the road surface could take the form of the concrete pavement panel described above or of another concrete pavement panel with an abrasion resistant surface.

In some forms, the method further comprises the step of casting a concrete support element, the concrete support element having a levelling surface and an underside surface. The concrete support element assists in the prevention of structural cracking in the panel as a result of overloading. In some forms, the concrete support element is cast such that the underside surface is in contact with a ground surface.

In some forms, the method further comprises the step of positioning levellers between the levelling surface of the concrete support element and the base surface of the concrete pavement panel.

In some forms, the levellers are configured such that they level the abrasion resistant wear surface. Levellers assist in levelling the panel surface such that it forms a flat roadway surface.

In some forms, the method further comprises the steps of arranging the concrete pavement panels such that are positioned in an abutting relationship. By providing multiple panels in an abutting relationship, the length of the road can be extended. Also, it may be beneficial to provide multiple small panels, potentially of varying shape, rather than one lengthy panel. Also, panels of varying shape allows the roadway to be adapted for corners.

In some forms, the method further comprises the step of locating a sealing element between the concrete pavement panels. Where the panels are positioning in an abutting relationship, it is likely that there will be a small gap between the panels. Inclusion of a sealing element, such as grout, prevents the edges of the panels from wearing and also inhibits the intrusion of debris between the panels.

In some forms, the method further comprises the step of locating the sealing element between the levelling surface of the concrete support element and the base surface of the concrete pavement panel. The sealing element assists in load transfer between the panel, the blinding slab and the subgrade.

In some forms, the method further comprises the step of holding the concrete pavement panels in the abutting relationship until the sealing element reaches a compressive strength of at least 10 MPa.

In some forms, the concrete support element is a blinding slab. In some forms, the blinding slab has a compressive strength of 25-30 MPa.

In some forms, another concrete support element is positioned between the blinding slab and the concrete pavement panel.

In some forms, the another concrete support element is a support slab with a compressive strength of 30-50 MPa.

In some forms, the levellers are levelling shims. In some forms, the levellers are levelling rails.

In some forms, the sealing element is grout or epoxy. Referring firstly to Figure 1, a concrete pavement panel is shown in the form of a wearing slab 1. The concrete pavement panel 1 has a wear surface arranged to form part of the surface of a roadway, shown in the form of road surface 3, and it is the surface of the concrete pavement panel that faces upwards from the ground and is subject to heavy vehicle activity. The wearing slab 1 is manufactured from ultra-high performance concrete (UHPC). UHPC is a type of concrete that is characterised by having a compressive strength greater than 120 MPa. UHPC typically has steel fibre re-inforcement in lieu of large diameter reinforcing bars. Steel fibres are commonly added to UHPC to provide post-cracking performance, but are not necessarily required in this application. The UHPC used in this application differs substantially from previous applications in comprising coarse aggregate of much larger diameter and containing a much larger proportion of coarse aggregate relative to the total volume of material used than is normal in UHPC.

The wearing slab 1 of the present disclosure includes high proportions of coarse aggregate 9 and fine aggregate 11 to produce a highly abrasion resistant road surface 3.

Coarse aggregate 9 is in the form of aggregate with a maximum nominal diameter of greater than or equal to 20mm. The quantity of coarse aggregate in the UHPC panel is typically greater than 1000kg/m ³ .

A number of cementitious mixtures have been formed and tested in order to determine a composition that is suitable for a roadway. Table 1 shows a range of cementitious mixture compositions that have been identified as being suitable for use as a highly abrasion resistant pavement surface. Cementitious mixtures A, B & C were precast to form concrete panels and all displayed very high (100+ MPa) to ultra-high (120+ MPa) compressive strength at 28 days either with or without special heat treatment.

Table 1 : Range of mixture proportions typically used in UHPC containing coarse aggregates (all quantities in kg/m ³ or L/m ³ for liquids).

Coarse aggregate 1160 1300 1680

Water/binder 0.18 0.185 0.17

Superplasticiser (L) 30 30 25

Compressive Strength (MPa) 124 128 145

Cementitious mixture A includes 140kg/m ³ of cement, 140kg/m ³ of silica fume, 420 kg/m ³ of fly ash, 42 kg/m ³ of silica flour, 515 kg/m ³ of coarse sand, 1160 kg/m ³ of coarse aggregate, a water/binder ratio of 0.18 and 30 L of superplasticiser. Cementitious mixture A has the advantage of a very high fly ash content resulting in low heat emission and a lower total cost associated with its manufacture. However, cementitious mixture A suffers the disadvantage of requiring a relatively long setting time and exhibits a slow rate of strength gain. Cementitious mixture A has a compressive strength of 124 MPa after 56 days.

Cementitious mixture B includes 300kg/m ³ of cement, 120kg/m ³ of silica fume, 180 kg/m ³ of fly ash, 45 kg/m ³ of silica flour, 520 kg/m ³ of coarse sand, 1300 kg/m ³ of coarse aggregate, a water/binder ratio of 0.185, and 30 L of superplasticiser. Cementitious mixture B has a faster setting time relative to cementitious mixture A. Cementitious mixture B has a compressive strength of 128 MPa after 28 days and 140 MPa after 91 days. Cementitious mixture B has displayed inferior wet properties relative to cementitious mixture A, exhibiting relatively greater stickiness. The high sand content results in a smoother finish at the exposed surface of the precast concrete panel such that the mixture displayed good levelling characteristics.

Cementitious mixture C includes 300kg/m ³ of cement, 105kg/m ³ of silica fume, 160 kg/m ³ of fly ash, 240 kg/m ³ of coarse sand, 1680 kg/m ³ of coarse aggregate, a water/binder ratio of 0.17 and 25 L of superplasticiser. Mixture C has a higher percentage of coarse aggregate relative to mixtures A and B. The high percentage of coarse aggregate gives mixture C the highest abrasion resistance. However, mixture C is not self-levelling and the exposed surface of the precast concrete panel is rough relative to mixtures A and B. Another advantage of mixture C is that it exhibits excellent strength development and has very low drying shrinkage (250 microstrain at 56 days). Cementitious mixture C has a compressive strength of 145 MPa. It is worth noting here that one factor that determines compressive strength of the example panels is the type and quantity of superplasticiser used in the mixture. While the range of panels shown have a compressive strength of 120 to 150 MPa, future development in the field of superplasticisers may lead to the manufacture of UHPC panels from similar mixtures that exhibit a higher compressive strength.

Previously, uneven distribution of aggregate in the manufacture of concrete panels is avoided during casting to ensure that the end product exhibits consistent strength

characteristics throughout. However, in at least one form of the present disclosure, uneven distribution and segregation are deliberately sought. The terms segregation and settling are terms that are interchangeably used in the industry and refers to segregation by particle size that occurs during settling. Segregation is usually a function of particle size, density and shape. The coarse aggregate 9 in the wearing slab 1 of the present disclosure is unevenly distributed through the panel with a higher proportion of the coarse aggregate 9 being in the region of the wear surface 3. During casting, the region of the wear surface may be the lower region of the cast panel, which when hardened is turned over to become the highly abrasion resistant wear surface 3. Coarse aggregate 9 has a maximum nominal diameter of between than 20mm and 40mm. The coarse aggregate 9 is caused to have a higher proportion in the region of the wear surface 3 as a result of settling of the coarse aggregate 9 during forming of the panel 1. Uneven distribution of the coarse aggregate is achieved by varying the water/binder ratio to achieve a degree of fluidity that results in segregation when the panel is agitated during casting. For example, a high water/binder ratio may produce a mixture that is more fluid, causing a large proportion of the aggregate to fall to the bottom of the panel, or settle, within the mixture. Conversely, a low water/binder ratio may produce a mixture that is less fluid, causing a small proportion of aggregate to fall to the bottom of the cast panel, or settle, within the mixture.

In addition to uneven distribution of the coarse aggregate 9 in the concrete panel, this process segregates the coarse aggregate 9 from the fine aggregate 11 and paste. During production, the coarse aggregate 9 falls to the lower surface of the concrete panel, while the fine aggregate and paste remains suspended higher up in the mixture. The result of said segregation is that the fine aggregate 11 and paste is segregated from the coarse aggregate 9 such that a higher portion of the fine aggregate and paste is in a region of the panel spaced away from the wear surface 3. The panels 1 are at least 150 mm thick to allow for in-service wear and sufficient strength during installation. When the panels are produced by casting, the panels may be turned over such that the lower surface of the panel during casting becomes the highly abrasion resistant wear surface when installed.

Referring now to Figs. 2 and 7, a method of forming a concrete pavement panel is shown. The concrete pavement panel has a wear surface that is arranged to form part of a surface of a roadway and has a compressive strength of greater than or equal to 120 MPa. The method of forming a concrete pavement panel comprises the steps of providing a suitable cementitious mixture containing at least 1000 kg/m ³ of coarse aggregate. The cementitious mixture may be any one of mixtures A, B or C, or another mixture that exhibits ultra-high performance and contains at least 1000 kg/m ³ of coarse aggregate such that the panel has a highly abrasion resistant wear surface.

The cementitious mixture is then cast at step 22 (also shown in Fig. 7) using formwork 7 to produce a panel, in the form of a UHPC wearing slab. Adequate conditions are then provided to allow the mixture to harden at step 26. The conditions can be met by any means known in the art, including allowing the panel to cure at room temperature and pressure or an elevated temperature. Prior to hardening 26, the coarse aggregate 9 is caused to unevenly distribute in the mixture such that a higher proportion of the coarse aggregate 9 is in the region of the wear surface 3. The wear surface 3 is the lower surface of the panel during casting.

The coarse aggregate is caused to unevenly distribute in the mixture by settling 24. Settling also causes the coarse aggregate 9 to be segregated from the fine aggregate 11 and paste within the panel such that a higher portion of the fine aggregate 11 and paste is suspended in the region of the panel spaced away from the wear surface 3. Settling 24 also causes a higher proportion of the coarse aggregate 9 to be in the region of the wear surface 3 during forming of the panel 1. The panel 1 produced using this method is a pre-cast concrete panel that exhibits ultra-high performance in that it has a compressive strength of at least 120 MPa. In addition to this, the method produces a concrete panel with a highly abrasion resistant wear surface. To exploit this effect, the panel uses the lower surface of the cast panel as the highly abrasion resistant wear surface 3 when installed.

Referring now to Figs. 3-6, a method for constructing a roadway from precast concrete pavement panels is shown. The method comprises at step 100 providing one or more UHPC pavement panels with a highly abrasion resistant wear surface 3 such as a panel described above. It should be noted that another concrete precast panel could also be installed to form part of a roadway surface using the disclosed method. Following the casting and hardening of the UHPC precast panels, the panels are turned-over at step 102, such that the wear surface 3 forms part of a road surface 34. The panel 1 has a base surface 35.

The surface of the sub-grade is then cleaned and a concrete support element, in the form of a blinding slab 36, is cast at step 104 onto the sub-grade 42 (shown in Figs. 3-4, and 6). Structural cracking that may result from overloading is not a concern when a panel is located over a deep blinding slab or over ground consisting of essentially undisturbed rock. In areas where deep cavities are present in the sub-grade 42 rock, a blinding slab is

preferentially cast in lieu of compacted fill. The blinding slab typically has a compressive strength of 25-30 MPa. It is necessary to use a moderate strength grout around the panels to facilitate removal and replacement if the panels wear out. The blinding slab 36 has a levelling surface, in the form of its upper surface 38, and an underside surface 40 that is in contact with a ground surface, in the form the sub-grade 42. Levellers, in the form of shims 44 or levelling rails 45 are then positioned at step 106 between the levelling surface 38 of the blinding slab and the underside surface 35 of the panel 1. The levellers 44 effectively level the precast panels 1 such that the wear surface 3 forms a flat roadway surface. Following the levelling of a single panel, further panels are arranged 108 such that they are positioned in an abutting relationship. Each panel is levelled using levelling shims 44 or a levelling rail 45.

Previously, concrete pavements suffered from shoulder breakdown at joints. Shoulder breakdown causes severe deterioration between the panels and at the edges of the panels. For this reason it is preferable to keep joints tightly closed to prevent shoulder breakdown. In addition, joint sealants can be used to keep debris out of the joint. Available sealants do not have sufficient strength and resilience to survive for long periods of time in highly abrasive applications. An emphasis of the disclosed method is therefore on joint tightness.

A sealing element 46, in the form of grout or epoxy, is then located at step 110 between the panels. The grout 47 has a compressive strength of approximately 30 MPa when hardened and effectively fills the gaps between and around the panels to prevent the infiltration of debris. The grout 47 is slow setting such that injection of the grout between the panels also allows the grout 47 to locate between the blinding slab 36 and the precast panel 1. This allows load transfer between the precast panel and the subgrade to prevent structural cracking of the panels. Further, in one form the width of the pre-cast panels is sufficient to preclude large vehicles, such as trucks, from driving over the grout used to secure the panels in place at the margins as this grout has relatively poor abrasion resistance. The panels are then held at step 112 in an abutting relationship for a sufficient length of time to allow the grout 47 to reach a compressive strength of at least 10 MPa to facilitate transfer of structural loads from vehicles into the blinding slab and the sub-grade.

As shown in Fig. 4, if a specific application requires it, another concrete support element, in the form of a second blinding slab 48 with a relatively high compressive strength of between 30-50 MPa can be positioned between the first blinding slab 36 and the precast concrete panel 1. The end result of the method of road construction disclosed is a highly abrasion resistant wear surface. Advantageously, replacement of the pavement panels is relatively easy. New panels of slightly smaller dimensions than the originals can be installed followed by re-grouting to secure them in place. To facilitate easy replacement, each panel may be fitted with lifting toggles placed near the centre between the axles of the passing vehicles to limit potential wear and damage at these points. Also, the panels of the present disclosure do not require any keys at the edges because structural load transfer requirements are non-existent and keys will prevent easy replacement of worn panels.

Use of pre-cast concrete panels for roadway surface production is advantageous for a number of reasons. Pre-casting can be undertaken using higher strength concrete than is feasible for cast-in-place concrete because of the availability of superior preparation and consolidation in a pre-casting yard. A compressive strength of between 120-160 MPa can be achieved in 56 days by normal curing, and thus high strength is available immediately upon installation.

In addition to this, pre-cast panels may be turned over once produced so that a smooth high density off-form finish acts as the wearing surface. Further, a slightly segregating mix may be utilised, which results in a concentration of abrasion-resistant aggregate in the upper wearing surface rather than at the bottom of the mix as would occur for cast-in-place concrete.

Further, pre-casting helps to ensure that all the shrinkage that the concrete is likely to experience will occur before the panels are installed. Joints will therefore remain more tightly sealed and resistant to the ingress of detritus causing wear. Also, pre-cast panels can be installed more rapidly and with greater precision than a cast-in-place slab in most circumstances. This results in rapid installation and maintenance of a roadway.

In the claims which follow and in the preceding description, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e., to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the disclosure.