The invention relates to a method of producing a concrete product incorporating rubber aggregate, and a concrete product incorporating rubber aggregate.
In the past few decades, disposal of scrap rubber has become a major environmental concern across the globe. Used tyres from the automotive industry forms the largest source of scrap rubber. Noting the growing prevalence of automotive transportation in for example developing countries, it is currently estimated that approximately 1 billion tyres are discarded annually worldwide. Currently, approximately 4 billion waste rubber tyres are located in stockpiles and landfills around the world.
Stockpiles of the waste rubber create serious environmental concerns. Waste rubber is not particularly biodegradable and can easily catch fire to release toxic fumes. Tyre stockpiles also provide breeding habitats for vermin, rats and mosquitoes resulting in a significant health risk to nearby communities. Landfilling and stockpiling of waste rubber is therefore undesirable and, in view of reduced landfill site availability, is becoming less feasible into the future.
Currently, most waste rubber is recycled as fuel in cement kilns, pulp, paper and electric utility boilers. However, as noted above, burning of waste rubber produces hazardous gases and is not environmentally friendly. New, environmentally friendly and cost-efficient uses of waste rubber remain very desirable.
Concrete is a widely used construction material. Its usage worldwide, ton for ton, is believed to be twice that of steel, wood, plastics, and aluminium combined. It is commonly formed from a matrix of aggregate, such as coarse gravel, crushed rocks and sand, and a binder such as Portland cement.
When used in this specification unless the context otherwise requires, the term ‘concrete’ is intended to relate not only to traditional Portland cement concretes but more broadly to any composite material involving a matrix of aggregate and a binder. Such concretes may include polymer concretes, asphalt concretes, hydraulic cement concretes generally, geopolymers, and other suitable building materials.
Given the amount of concrete used world-wide, concrete is a heavy consumer of natural resources such as rocks, gravel and sand, as well as lime. Finding and using sustainable alternatives to concrete, or components of concrete, is therefore clearly desirable. In this respect many Chinese local authorities have made it mandatory to utilize recycled concrete as aggregate in new construction projects from 2019. Incorporating waste materials into concrete not only slows the depletion of natural resources and dumping of waste, but may also reduce construction costs.
Waste rubber has previously been investigated in the manufacture of concrete. Rubber powder, crumb rubber, and tyre chips have been used as respective substitutes for cement, and fine and coarse aggregates. However, while incorporating waste rubber into concrete may be considered environmentally friendly, the resulting concrete has demonstrated poor performance characteristics as now exemplified.
In previous studies concrete, wherein 100% of natural coarse aggregates were replaced with waste tyre chips, was found to provide an 85% reduction in compressive strength and a 50% reduction in split tensile strength when compared with similar traditional concrete. In similar studies concrete wherein 100% of natural fine aggregates was replaced with crumb rubber, was found to provide a 65% reduction in compressive strength and a 50% reduction in split tensile strength. The reduction in concrete strength was shown to depend on the size and amount of rubber particles incorporated into the concrete such that the larger the rubber particles and the greater the amount of rubber particles used, the lower the resulting concrete strength. Addition of rubber in concrete has also been found to reduce the elastic modulus and flexural strength of the concrete.
While the incorporation of rubber into concrete has nevertheless been shown to provide some positive performance attributes including: improved post-peak behaviour, ductility, dynamic properties, resistance to cracks and freeze-thaw attack when as compared to conventional concrete, the resulting loss in strength as described above has meant that recycling of waste rubber into concrete has traditionally been considered unfeasible.
Various researchers have sought to improve the performance characteristics of concrete incorporating rubber by surface treatment of waste rubber particles. Rubber particles have for example been surface treated with sodium hydroxide solution or saline coupling agent. In other treatments rubber particles have been pre-coated with blended cement. Among these techniques, surface treatment of rubber particles with a NaOH solution is considered to provide the best results.
Surface treatment of rubber particles with NaOH solution has been found to improve the bond between rubber particles and cement paste such that the performance of concrete incorporating treated rubber is comparatively better than concrete incorporating untreated rubber. One previous study reported a 17% increase in compressive strength of concrete incorporating NaOH-treated rubber particles with compared with concrete incorporating untreated waste rubber. However, the strength of concrete incorporating the NaOH-treated rubber still remained much lower than that of conventional concrete.
US patent application 2005/0096412 A1, the entire disclosure of which is incorporated by reference, discloses a concrete composition comprising rubber aggregate having a distinct geometric shape and formed by cutting rubber tyres with special saws or water jets. However, use of specialised cutting tools suggests increased costs and does not appear to of itself overcome concrete performance issues outlined above.
EP patent 2694449, the entire disclosure of which is incorporated by reference, describes a method of producing rubberised concrete in which crumb rubber is partially oxidised to provide hydrophilic surface properties and a gas binding agent which is said to assist with bonding of rubber particles to other components of concrete. Like other surface treatments, it is not clearly apparent that the disclosed technology provides performance properties similar to conventional concrete.
The utilization of rubber in concrete therefore remains limited and it would be desirable, though not essential, to provide a concrete product which incorporates rubber while providing satisfactory strength characteristics.
The above discussion of background art is included to explain the context of the present invention. It is not to be taken as an admission that the background art was known or part of the common general knowledge at the priority date of any one of the claims of the specification.
According to a first aspect of the invention, there is provided a method of producing a cast concrete product, the method comprising:
Optionally, the method comprises casting the concrete slurry at a pressure of between 2-50 MPa, optionally between 5-35 MPa, further optionally between 6.9-27.7 MPa.
Optionally, the method comprises selecting a pressure under which to cast the concrete slurry based upon the amount of rubber fragments within the concrete slurry to be cast. Further optionally, the method comprises selecting a pressure under which to cast the concrete to reduce the volume of the concrete slurry by approximately the volume of rubber aggregate within the concrete slurry prior to casting under pressure.
Optionally, wherein pressure is sustained substantially to keep concrete volume unchanged throughout casting of the concrete slurry.
Optionally, the method comprises casting the concrete slurry under pressure for between 3-48 hours, optionally between 6-36 hours, further optionally for substantially 24 hours.
Optionally, following casting the cast concrete product is cured at atmospheric pressure, at between 10-30° C. and at 50-100% humidity for between 10-30 days.
Optionally, the concrete slurry comprises Portland cement.
Optionally, the rubber aggregate has not previously undergone chemical treatment to alter its surface properties, such as by sodium hydroxide treatment. Alternatively, the rubber aggregate has undergone chemical treatment to alter its surface properties.
Optionally, the rubber aggregate is produced from waste materials, optionally waste tyres. Alternatively, the rubber aggregate is produced from new or previously unused rubber.
Optionally, the method further comprises introducing reinforcement mesh or fibres into the mould or slurry prior to casting.
According to a further aspect of the invention, there is provided a cast concrete product produced according to the first aspect of the invention.
Optionally, the cast concrete product is either: a masonry brick or block such as a Bessemer block, a pre-fabricated pipe, a pre-fabricated construction beam, a pre-fabricated construction wall, or a prefabricated construction slab.
Throughout this specification and the claims which follow, unless the context requires otherwise, the word “comprise” and variations thereof such as “comprises” and “comprising”, will be understood to include the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or groups of integers or steps.
It will be convenient to further describe embodiments of the invention, as well as research relating to the invention, with reference to the accompanying drawings. Other embodiments are possible, and consequently, the particularity of the accompanying drawings is not to be understood as superseding the generality of the preceding description of the invention.
Research and experiments performed by the inventors in developing the invention are now discussed.
The following materials were used to prepare concrete slurries utilised in experiments performed by the inventors:
As shown in
To prepare concrete specimens for experimentation, the inventors replaced a portion of crushed granite with coarse rubber aggregate at nine different proportions by volume (i.e., 0%, 10%, 15%, 20%, 30%, 40%, 50%, 80% and 100%). The constituents of each slurry are further detailed by volume in Table 2 below, whereby for example:
‘R10’ and ‘R20’ each respectively refer to replacement of 10% and 20% by volume of crushed granite with coarse rubber aggregate; and
‘R10-U’ refers to a concrete specimen that underwent casting without pressure, while ‘R10-C’ refers to a concrete specimen that underwent casting under pressure.
More generally, unless the context otherwise requires, throughout this specification:
All concrete slurries were prepared using a double shaft concrete mixer following practices set out in ASTM C192:2016 as discussed below. The slump of each concrete slurry was observed to be between 25-50 mm. The addition of coarse rubber aggregate was not observed to affect the workability of concrete slurry and no bleeding or segregation was observed in any concrete slurry.
After mixing, the concrete slurry was filled into a specially designed mould 8 up to a height calculated based on the volume of coarse rubber aggregate in the cement slurry (see further discussion below). After filling the mould 8, force was applied by a jack 9 to compress the R-concrete slurries for a period of 24 hours.
For R-concrete specimens in which coarse rubber aggregate replaced crushed granite at between 0 and 40% by volume, the maximum pressure applied ranged from between 6.9 MPa to 27.7 MPa so as to ensure a reduction in cement slurry volume equal to volume of rubber in the concrete slurry when unpressurised. That is, where a R-concrete slurry for example incorporated 500 mL of coarse rubber aggregate when unpressurised, the jack 9 was configured to provide a pressure which reduced the overall volume of the R-concrete slurry by 500 mL. For R-concrete slurry incorporating between 50%-100% coarse rubber aggregate, the maximum load capacity of the jack limited the maximum pressure available to 27.7 MPa.
Noting that the required pressure load may reduce while concrete gains strength during casting, a pressure load to keep the concrete volume unchanged during casting was maintained for 24 hours, after which the R-concrete specimens 10 were de-moulded. Concrete specimens were all then further cured for 28 days in a moist curing chamber with a temperature of 20° C. and relative humidity of 95%.
In total, 24 R-C concrete and 27 R-U concrete specimens were cast. All concrete specimens where configured to have the same size of 150 mm (diameter)×300 mm (height). For each combination (e.g. of R10-C or of R10-U), three identical specimens were cast and tested.
Uniaxial compression tests were performed using an MTS machine having a capacity of 3000 kN. As shown in
smaller elastic modulus) with increased use of coarse rubber aggregate; and similar trends can be observed in
All the R-C concrete specimens demonstrated a concrete strength significantly higher than that of corresponding R-U concrete specimens. The concrete strength of the R50-C concrete specimen was found to be close to that of the R15-U concrete specimen, thereby demonstrating the effectiveness of casting under pressure to enhance rubber concrete performance.
For R-C concrete, an increase in concrete strength was observed compared with NAC for specimens at a rubber replacement ratio up to 30%. For example, R10-C and R20-C specimens demonstrated respective 24% and 35% increases in concrete strength when compared to NAC specimens. However, a reduction in concrete strength of R-C concrete specimens was still observed compared with NAC for replacement ratios of rubber higher than 30%.
For R-C concrete specimens, a reduction in peak strain was observed with increased incorporation of coarse rubber aggregate. R10-C, R30-C, R50-C, and R100-C concrete specimens respectively demonstrated 25%, 31%, 39% and 34% reductions in peak strain when compared to NAC specimens. All R-U concrete specimens demonstrated higher peak strains than corresponding R-C concrete specimens. Without wishing to be bound by theory, the reduction in peak strain of R-C concrete specimens was attributed to an increased elastic modulus.
For R-U concrete specimens, no significant effect on ultimate strain was observed up to 40% replacement ratio of coarse rubber aggregate when compared to NAC specimens. However, an increase in an ultimate strain of R-U concrete specimens was observed for R50-U and R100-U concrete specimens compared to NAC specimens. For instance, the NAC specimens had an average ultimate strain of 0.0032, which increased to 0.0038, 0.0051, 0.0093 for R50-U, R80-U and R100-U specimens, respectively.
For R-C concrete specimens, a reduction in ultimate strain was observed with increased replacement ratio of rubber. For instance, R10-C and R30-C specimens demonstrated 41% and 46% reductions in ultimate strain when compared to NAC specimens. All R-U concrete specimens demonstrate an ultimate strain higher than corresponding R-C concrete specimens.
The modulus of elasticity of all concrete specimens was determined from the initial slope of the axial stress-strain curves.
For R-C concrete specimens, an increase in elastic modulus was observed for specimens incorporating a rubber replacement ratio up to 15%. For instance, R10-C and R15-C specimens demonstrated 9% and 38% increases in elastic modulus as compared to NAC specimens. A reduction in elastic modulus of R-C concrete specimens was observed with increasing rubber replacement ratios after reaching its peak at 15% rubber replacement ratio. Still, specimens with a rubber replacement ratio up to 30% demonstrated an elastic modulus higher or close to NAC specimens.
All R-C concrete specimens demonstrated an elastic modulus significantly higher than corresponding R-U concrete specimens. The elastic modulus of R50-C specimens was higher than R10 specimens, which demonstrated the effectiveness of the casting under pressure in enhancing the rigidity of R-concrete.
Toughness (i.e., energy absorption capacity) of concrete specimens was determined as the area under the stress-strain curves up to the ultimate strain of concrete specimens.
R-C concrete specimens also demonstrated an initial increase and then reduction in toughness with increasing in rubber replacement ratio. The maximum toughness was reached at a rubber replacement ratio of 15%. The toughness of R-U concrete specimens was similar to, but generally higher than corresponding R-C concrete specimens. All R-concrete specimens demonstrated toughness values lower than NAC specimens.
As toughness is affected by the compressive strength of concrete specimens, specific toughness (i.e., the ratio of toughness to the compressive strength) was considered a better measure of toughness by the inventors.
For R-C concrete specimens, a small reduction in specific toughness was observed with the increasing rubber replacement ratio up to 40%. This trend reversed from 50% rubber replacement ratio. All R-U concrete specimens demonstrated specific toughness significantly higher than corresponding R-C concrete specimens.
Scanning electron microscopy (SEM) was also performed on the NAC, R-C and R-U concrete specimens obtained after compression testing. The samples were oven dried and gold coated before analysis using the Quanta FEG 250 environmental scanning electron microscope.
Concrete material properties are often related and the relationship between concrete strength and other material properties such as Young's modulus and peak strain are commonly used in engineering designs. Although R-C concrete can achieve similar strength and Young's modulus to NAC, the relationship between material properties are significantly different now discussed.
Two compression conditions were studied by the present inventors:
As shown in
The discoveries of the present inventors can significantly enhance mechanical properties of R-concrete while providing reduced manufacturing costs. A comparison of the cost of raw materials required for a 390 mm×190 mm×190 mm Besser concrete block—as shown in
The novel compression technology for manufacturing rubber concrete can be used to make prefabricated construction materials such as concrete blocks/bricks, pavement blocks, and other concrete elements, e.g. wall panels, beams, slabs, road barriers etc. Aside from the significant advantages in facilitating eco-friendly constructions, the cost of the products made by this technology may be lower than traditional/existing concrete products. Just as importantly, existing manufacturing processes and facilities can generally be retained subject to the pressure casting steps of the invention.
Comparing the images of compressed concrete and uncompressed concrete in
While the experiments described above were made in respect of coarse rubber aggregate, concrete may also be produced in which rubber crumb is incorporated to concrete slurry as fine rubber aggregate, to for example replace all or a proportion of sand otherwise found in Portland cement concrete. In doing so, the resulting concrete product may comprise fine rubber aggregate, coarse rubber aggregate, or both. Additionally, the concrete product may comprise metal reinforcement or other additives as desired or deemed appropriate. Reinforcement, such as reinforcement mesh (commonly referred to in Australia as ‘reo’), which may for example be made of metal may be incorporated into the concrete slurry or introduced separately to a casting mould prior to casting under pressure. Alternatively (or additionally) reinforcement fibres, such as glass fibres, polymer fibres (e.g. Nylon or polypropylene fibres) cellulosic fibres, or metal fibres, may be incorporated into the concrete slurry prior to casting. It is envisaged that other additives may be incorporated into the concrete slurry or cast concrete product.
It will be understood to persons skilled in the art of the invention that modifications may be made without departing from the spirit and scope of the invention. The embodiments and/or examples as described herein are therefore to be considered as illustrative and not restrictive.
The present application is a § 371 national phase entry of PCT International patent application Serial No. PCT/CN2019/110035, filed Oct. 9, 2019.
Filing Document | Filing Date | Country | Kind |
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PCT/CN2019/110035 | 10/9/2019 | WO |