Patent Description:
Metallurgical slag is an abundant waste material that is usually landfilled. Metallurgical slag may act as a binder material under appropriate conditions. Finding new uses for metallurgical slag, including steel slag, are required.

Document <CIT> discloses a method for producing a slag based concrete comprising mixing steel slag, filler and water, compacting the moulded mixture and curing the formed block with CO<NUM>.

Development of concrete products, that are optionally reinforced, and made from a metallurgical slag as the main binder and carbon dioxide with the wet-cast method is explained herein.

In accordance with one aspect there is provided a method of producing a wet-cast slag-based concrete product comprising steps of: providing a composition for a non-zero-slump concrete, the composition comprising a slag-based binder, an aggregate and water; mixing the slag-based binder, the aggregate and the water to produce the non-zero-slump concrete comprising a first water to binder ratio by weight of greater than <NUM>; casting the non-zero-slump concrete by transferring the non-zero-slump concrete into a mould; setting the non-zero-slump concrete partially or fully within the mould to produce a slag-based intermediate comprising a second water to binder ratio by weight that is less than the first water to binder ratio by weight; demoulding the slag-based intermediate to produce a demoulded intermediate; pre-conditioning the demoulded intermediate to produce a demoulded conditioned slag-based intermediate comprising a third water to binder ratio by weight that is less than the first water to binder ratio by weight and that is also less than the second water to binder ratio by weight; and curing the demoulded conditioned slag-based intermediate with carbon dioxide to activate the conditioned slag-based intermediate and produce the wet-cast slag-based concrete product, wherein the step of casting of the non-zero-slump concrete composition is free of pressing/compaction.

In accordance with another aspect there is provided the method described herein, wherein the slag-based binder is a slag - free of or mixed with at least one other binder selected from the group further consisting of fly ash, calcinated shale, silica fume, zeolite, GGBF (Ground Granulated Blast Furnace) slag, limestone powder, hydraulic cements and non-hydraulic cements.

In accordance with yet another aspect there is provided the method described herein, wherein the slag is selected from the group consisting of a steel slag, a stainless steel slag, a basic oxygen converter sludge, blast furnace sludge, a by-product of zinc, iron, copper industries and combinations thereof.

In accordance with still yet another aspect there is provided the method described herein, further comprising a reinforcing step of placing a reinforcing material into the mould before the casting step.

In accordance with still yet another aspect there is provided the method described herein, wherein the reinforcing material is carbon steel, stainless steel and/or fiber reinforced polymer (FRP) reinforcement bars.

In accordance with still yet another aspect there is provided the method described herein, wherein a cumulative calcium silicate content of the slag is at least <NUM> weight%.

In accordance with still yet another aspect there is provided the method described herein, wherein the pre-conditioning increases porosity of at least <NUM>% of volume of the wet-cast slag-based concrete.

In accordance with still yet another aspect there is provided the method described herein, wherein the non-zero-slump concrete has a slump value in a range of <NUM> to <NUM>.

In accordance with still yet another aspect there is provided the method described herein, wherein the non-zero-slump concrete has a compaction factor test for the fresh concrete must find a value in the range of <NUM> to <NUM>.

In accordance with still yet another aspect there is provided the method described herein, wherein the steel slag is selected from the group consisting of reducing steel slag, oxidizing steel slag, converter steel slag, electrical arc furnace slag (EAF slag), basic oxygen furnace slag (BOF slag), ladle slag, fast-cooled steel slag and slow-cooled steel slag and combinations thereof.

In accordance with still yet another aspect there is provided the method described herein, wherein the wet-cast slag-based concrete is further processed to a product selected from the group consisting of precast, reinforced and non-reinforced concrete pipes, box culverts, drainage products, paving slabs, floor slabs, traffic barriers, walls manholes, retaining wall, pavers, tiles, and shingles.

In accordance with still yet another aspect there is provided the method described herein, wherein the wet-cast slag-based concrete comprises of a slag content of at least <NUM>% by weight.

In accordance with still yet another aspect there is provided the method described herein, wherein the non-zero-slump concrete further comprises at least one accelerator, retarder, viscosity modifying agent, air entertainer, foaming agent, ASR (alkali silicati reaction) inhibitor, anti-wash-out, corrosion inhibitor, shrinkage reducer, concrete crack reducer, plasticizer, super plasticizer, sealer, paint, coating, water reducer, water repellant, efflorescence control, polymer powder, polymer latex and workability retainer.

In accordance with still yet another aspect there is provided the method described herein, wherein the non-zero-slump concrete further comprises at least one cellulose fiber, glass fiber, micro synthetic fiber, natural fiber, polypropylene (PP) fiber, polyvinyl alcohol (PVA) fiber and steel fiber.

In accordance with still yet another aspect there is provided the method described herein, wherein the CO<NUM> curing is free of additional external sources of heat/energy.

In accordance with still yet another aspect there is provided the method described herein, wherein the demoulded conditioned slag-based intermediate is cured in a chamber/enclosed space/vessel/room with a gas containing a concentration of CO<NUM> of at least <NUM>% by volume.

In accordance with still another aspect there is provided the method described herein, wherein in producing <NUM><NUM> of the wet-cast slag-based concrete product, the first water to binder ratio of the non-zero-slump concrete was <NUM> with a time for the setting the non-zero-slump concrete of <NUM> hours.

In accordance with still another aspect there is provided the method described herein, wherein the producing <NUM><NUM> of the wet-cast slag-based concrete product began with a mass of <NUM> or <NUM> of the slag.

In accordance with still yet another aspect there is provided the method described herein, wherein the demoulding occurs when the demoulded intermediate has a compressive strength of at least <NUM> MPa.

Reference is now made to the accompanying figures, in which:.

Traditionally, newly sintered Portland cement is used as the binder in concrete production, and wet-cast cement-based precast concrete products are commonly cured with heat and steam. The present innovation of wet-cast slag-based concrete in contrast uses by-products of metallurgical plants and in a preferred embodiment - steelmaking factories as the main binder to replace Portland cement in production of concrete and precast products. In addition, carbon dioxide is used as an activator to cure the concrete and is sequestered in the process. In preferred embodiment, no additional heat or steam are needed during the CO<NUM> curing process. The proposed wet-cast slag-based concrete products, that are optionally reinforced, may show equal or superior mechanical and durability properties when compared to the traditional cement-based precast products, while their production would reduce greenhouse gas emissions to the atmosphere. The proposed innovation would also reduce consumption of natural resources, both as conventional cement is not used in the slag-based concrete products and as a lower amounts of aggregate content are needed in the slag-based concrete products. Finally, the production of wet-cast slag-based concrete products, optionally reinforced, according to the proposed innovation may increase production rate at the precast concrete making facilities.

The main binder in the production of wet-cast slag-based concrete <NUM> is a slag <NUM> that in a preferred embodiment derives from steel or stainless steel production. Other by-product materials from zinc, iron, and copper production can also be considered as the slag <NUM>.

Various slags <NUM> can be collected from steel factories that practice different methods of steel production. Among the types of slag <NUM> that can be incorporated as the main binder in production of wet-cast slag-based concrete described herein is: stainless steel slag, reducing steel slag, oxidizing steel slag, converter steel slag, electrical arc furnace slag (EAF slag), basic oxygen furnace slag (BOF slag), ladle slag, fast-cooled steel slag, slow-cooled steel slag, basic oxygen converter sludge, blast furnace sludge and combinations thereof.

The calcium oxide content by weight of slag <NUM> in a preferred embodiment is more that <NUM>%, preferably more than <NUM>%, preferably more than <NUM>%. The silica oxide content by weight in a preferred embodiment is more than <NUM>%, preferably more than <NUM>%, preferably more than <NUM>%. The total iron oxide content of slag in a preferred embodiment is less than <NUM>%, preferably less than <NUM>%. Steel slag <NUM> in a preferred embodiment has a cumulative calcium silicate content of at least <NUM>% and a free lime concentration of less than <NUM>%, and preferably less than <NUM>% slag. The bulk density of the slag <NUM> in a preferred embodiment has a range of <NUM> to <NUM>/cm<NUM> and an apparent density may vary from <NUM> to <NUM>/cm<NUM>.

The slag <NUM> may be ground to a smaller size (if required) before being incorporated into the wet-cast slag-based concrete mix described herein. Grinding the slag <NUM> can be performed with any mechanical machine such as a ball mill, rod mill, autogenous mill, SAG mill, pebble mill, high pressure grinding rolls, VSI or tower mill. The grinding process can be executed either wet or dry. While a dry size reduction process is preferred, if the wet process is chosen for grinding the slag, the ground slag can be either dried completely or semi-dried after grinding. Passing the slag through a classifier(s) is an alternative option to obtain slag <NUM> with a smaller particle/grain size. The classifiers used are known in the art and include but are not limited to : screens; centrifuges and cyclones.

Ground or classified slags <NUM> in a preferred embodiment pass through a mesh#<NUM> (<NUM> microns), preferably a mesh#<NUM> (<NUM> microns), preferably a mesh#<NUM> (<NUM> microns), preferably a mesh#<NUM> (<NUM> microns) each of which can be used alone or in combination with at least one other binder <NUM>. Sieves may be utilized to screen slags either after or before grinding. Thus, one or combination of grinding and screening methods can be executed in order to obtain slag <NUM> with a proper particle size distribution.

The slag <NUM> may be pulverized and/or screened to a Blaine fineness of at least <NUM><NUM>/kg and preferably, <NUM><NUM>/kg, and preferably at least <NUM><NUM>/kg. In a preferred embodiment the slag <NUM> in slag-based wet concrete, fifty percent of slag is smaller than <NUM> microns (D50=<NUM>), preferably smaller than <NUM> microns (D50=<NUM>), preferably smaller than <NUM> microns (D50=<NUM>), preferably smaller than <NUM> microns (D50=<NUM>), preferably smaller than <NUM> microns (D50=<NUM>), preferably smaller than <NUM> microns (D50=<NUM>).

The free lime content of the slag <NUM> may be reduced with any standard known method in the prior art before it is incorporated into the mix. Alternatively, the slag can first be aged to reduce its free calcium oxide (free lime) content and then incorporated into the mix. Slag <NUM> content of wet-cast slag-based concrete should be no less than <NUM>% of the weight of concrete, preferably no less than <NUM>% of the weight of the wet-cast slag-based concrete or the non-zero-slump concrete composition.

The slag-based binders <NUM> may further comprise: a slag alone (i.e. a slag that is-free of another binder) or be a combination of slag with at least one other binder <NUM>, such as cementitious materials/pozzolanic materials. As an example, slag <NUM> can be mixed with at least one other binder <NUM> producing a slag-based binder <NUM> further comprising: fly ash, calcinated shale, silica fume, zeolite, GGBF (Ground Granulated Blast Furnace) slag, limestone powder, hydraulic cements, non-hydraulic cements and combinations thereof.

Various types of aggregate <NUM> - including natural or artificial normal weight and lightweight aggregates - can be incorporated into the slag-based wet concrete product as filler in the production of wet-cast slag-based concrete product. Examples of potential lightweight aggregates includes natural lightweight aggregate (e.g. pumice), expanded clay aggregate, expanded shale aggregate and expanded iron slag aggregate. Other usable aggregates include: crushed stone, manufactured sand, gravel, sand, recycled aggregate, granite, limestone, quartz, chalk powder, marble powder, quartz sand and artificial aggregate. These aggregates are incorporated into the mix as fine and/or coarse aggregates. Aggregate content can be as high as <NUM>% of the weight of the wet-cast slag-based concrete or the non-zero-slump concrete composition.

The proposed slag-based wet concrete <NUM> is a workable concrete. Enough water should be added to the dry ingredient in order to produce a wet concrete (in contrast with slump-zero concrete). The required water content depends on the grain size of the slag chosen as the main binder and on the moisture content of the aggregates and content of binder. Finer ground slags absorb more water, so a higher water content would be required to produce wet concrete. Water-to binder ratio, in mass, can be <NUM>, preferably <NUM>, preferably <NUM>, preferably <NUM>, preferably <NUM>, preferably <NUM>, preferably <NUM>, or preferably <NUM>. For example, for the binder consisting of only slag with D50 of <NUM> microns, the water to binder ratio of <NUM> can result in a workable wet concrete. It may be the case that no additional water is required in the mix if the aggregates are very wet.

Chemical admixtures <NUM> can be introduced into the mix if required. Chemical admixtures <NUM> when introduced into the mix satisfy specific properties. Possible chemical admixtures <NUM> include but are not limited to: accelerators, retarders, viscosity modifying agents, air entertainers, foaming agents, ASR (alkali silica reaction) inhibitors, anti-wash-out, corrosion inhibitors, shrinkage reducers, crack reducers, plasticizers, super plasticizers, water reducers, water repellants, efflorescence controls and workability retainers.

Fibers can be added if required to the slag-based wet concrete. One or combination of cellulous fiber, glass fiber, micro synthetic fibers, micro synthetic fibers, natural fibers, PP fibers, PVA fibers and steel fibers can be incorporated into the mix.

The "zero-slump concrete" is defined as a concrete of stiff or extremely dry consistency showing no measurable slump after removal of the slump cone. A standard exemplary slump test is ASTM C143, for Hydraulic-Cement Concrete. A non-zero-slump concrete <NUM> is a concrete that is not stiff nor extremely dry consistency showing a measurable slump after removal of the slump cone by a test such as ASTM C143. The slump values herein are assessed using the method described in the ASTM C143 standard.

The method <NUM> of producing a wet-cast slag-based concrete <NUM> can be adapted to produce a variety of products including but not limited to precast, reinforced concrete pipes, box culverts, drainage products, paving slabs, floor slabs, traffic barriers, walls, manholes, precast non-reinforced concrete (plain) pavers, retaining walls, tiles and shingles. The products shall satisfy local and national standards and codes.

Referring to <FIG>, one embodiment of a method <NUM> of producing a wet-cast slag-based concrete <NUM> is provided.

The method <NUM> of wet-cast slag-based concrete <NUM> begins by providing a composition of a non-zero-slump concrete <NUM> and uniformly mixing <NUM> all ingredients of a composition that include but are not limited to : a slag <NUM> and an optional at least one other binder <NUM> (providing a slag-based binder <NUM>), an aggregate <NUM>, chemical admixtures <NUM>, fibers <NUM> and water <NUM>. The water-to-binder ratio of the wet-cast slag-based concrete <NUM> used in this innovation should be higher than the water content of dry-cast or zero-slump concrete. In a preferred embodiment the mixed non-zero-slump concrete <NUM> has a first water to binder ratio by weight of greater than <NUM>, preferably <NUM>, preferably <NUM>, preferably <NUM>, preferably <NUM>, preferably <NUM>, preferably <NUM>, preferably <NUM>, preferably <NUM> or preferably <NUM>. The terms "water to slag-based binder ratio by weight" and "water to binder ratio by weight" are equivalents.

The non-zero-slump concrete <NUM> will preferably have a slump range of <NUM> to <NUM>. The non-zero-slump concrete <NUM> is preferably workable for at least <NUM> minutes. The mixing <NUM> should ensure that the non-zero-slump concrete <NUM> is free of signs of segregation or bleeding. The compaction factor test for the non-zero-slump concrete <NUM> in a preferred embodiment is in a range of <NUM> to <NUM>. The temperature of non-zero-slump concrete <NUM> before casting is preferably <NUM> to <NUM>. The fresh non-zero-slump concrete <NUM> in a preferred embodiment has an air void content of measured by any conventional method (an exemplary standardized test is ASTM C231 for Air Content of Freshly Mixed Concrete by the Pressure Method)should not exceed <NUM>% of the volume of concrete. The compaction factor test is described in BS <NUM>-<NUM>:<NUM> and BS EN <NUM>-<NUM>:<NUM> (BS EN <NUM>-<NUM>:<NUM>, Testing fresh concrete Part <NUM>: Degree of compatibility). The non-zero-slump concrete <NUM> appropriately mixed is now ready for transfer to casting.

In a preferred embodiment before casting the non-zero-slump concrete <NUM> the mould is prepared and reinforcing material such as, carbon steel, stainless steel and/or FRP reinforcement bars are placed inside the mould, if required. The diameter of the bars may vary from <NUM> to <NUM> with yield strength in the range of <NUM> MPa to <NUM> MPa. The reinforcements to be designed in accordance with codes and standards.

The freshly prepared non-zero-slump concrete <NUM> is transferred by appropriate means and cast in a prepared mould with any known methods in the prior arts. The mould can be made of steel, iron, aluminum, plastic, FRP or other material. The mould should be pre-lubricated prior to casting in order to facilitate the demoulding process <NUM>. The wet-cast concrete or the slag-based intermediate <NUM> is consolidated within the mould by internal or external vibrators for no more than <NUM> seconds. The wet-cast concrete or the slag-based intermediate <NUM> does not need to be pressed or compacted inside the mould. That is the process is free of being pressed or compacted. The slag-based intermediate <NUM> is allowed to partially or fully set within the mould with a loss of water <NUM>.

The mould is kept at the ambient temperature and humidity, allowing free water <NUM> to gradually evaporate, and allows the partial or full hydration and setting of the binder. The rate of evaporation depends on the temperature, relative humidity, initial water content of the non-zero-slump concrete <NUM> mix, surface area of the product and air flow if the mould is exposed to wind. The hydration and setting rate depend on the ingredients and chemical composition of the slag-based binder <NUM>.

In addition to natural evaporation, in a preferred embodiment one or a combination of evaporation and/or heating <NUM> with heating elements or drum heaters or floor heating mats or fans or heaters or blowers or fan heaters can be used to accelerate the evaporation rate. The heating elements/wires or floor heating mats or drum heaters are installed so as to cover the exterior surfaces of the mould. The elements heat up the mould's walls and eventually increase the evaporation process to reduce the moisture content of the concrete. Fans, heaters, fan heaters and blowers, are best placed facing toward the slag-based intermediate <NUM> free surface, which may be its upper surface. These casting <NUM> steps may continue until initial water-to-binder ratio is reduced by up to <NUM>%, preferably <NUM>%, preferably <NUM>%, preferably <NUM>%, preferably <NUM>%, preferably <NUM>%, preferably <NUM>%, preferably <NUM>%, preferably <NUM>% or preferably <NUM>%. The increase of porosity defined in terms of volume created within the demoulded intermediate <NUM> by either of the above casting <NUM> methods in concrete is <NUM>%, preferably <NUM>%, preferably <NUM>%, preferably <NUM>%, preferably <NUM>%, preferably <NUM>%, preferably <NUM>%, preferably <NUM>% or preferably <NUM>% of the concrete volume. The slag-based intermediate <NUM> eventually attains a second water to binder ratio by weight that is less than the first water to binder ratio by weight of the non-zero-slump concrete <NUM>.

Upon demoulding <NUM> a demoulded intermediate <NUM> is produced. The slag-based intermediate <NUM> can set inside the mould for at least <NUM> hours but up to <NUM> days before demoulding. Demoulding may be undertaken in a preferred embodiment when the compressive strength of the concrete is at least <NUM> MPa as the result of the hydration/setting process.

The process step of pre-conditioning <NUM> reduces the water content of (the slag-based intermediate <NUM> now) the demoulded intermediate <NUM> even further to a third water to binder ratio by weight prior to CO<NUM> curing <NUM>. The demoulded intermediate <NUM> is kept at the ambient temperature and humidity, allowing free water <NUM> to gradually evaporates. The rate of evaporation of the demoulded intermediate <NUM> depends on the temperature, relative humidity, its initial water content, surface area of the product and air flow if the mould is exposed to wind. The pre-conditioning step of the demoulded intermediate <NUM> can be undertaken in a sealed room, enclosed space chamber or vessel.

In addition to natural evaporation, in a preferred embodiment one or a combination of evaporation and/or heating <NUM> with heating elements or drum heaters or floor heating mats or fans or heaters or blowers or fan heaters can be used to accelerate the evaporation rate. The heating elements/wires or floor heating mats or drum heaters are installed so as to cover the exterior surfaces of the demoulded intermediate <NUM>. The elements heat up the demoulded intermediate's <NUM> walls and eventually increase the evaporation process to reduce the moisture content of the concrete. Fans, heaters, fan heaters and blowers, are best placed facing toward the demoulded intermediate's <NUM> free surface, which may be its upper surface. These preconditioning <NUM> steps may continue until initial water-to-binder content is reduced by up to <NUM>%, preferably <NUM>%, preferably <NUM>%, preferably <NUM>%, preferably <NUM>%, preferably <NUM>%, preferably <NUM>%, preferably <NUM>%, preferably <NUM>% or preferably <NUM>%. The increase of porosity defined in terms of volume created within the demoulded intermediate <NUM> by either of the above pre-conditioning <NUM> methods in concrete is <NUM>%, preferably <NUM>%, preferably <NUM>%, preferably <NUM>%, preferably <NUM>%, preferably <NUM>%, preferably <NUM>%, preferably <NUM>% or preferably <NUM>% of the concrete volume. The pre-conditioning <NUM> produces a demoulded conditioned slag-based intermediate <NUM> with a third water to binder ratio by weight. The third water to binder ratio by weight is less than the first water to binder ratio by weight (of the non-zero-slump concrete <NUM>) and is also less than the second water to binder ratio by weight (of the slag-based intermediate <NUM>).

At the end of the pre-conditioning <NUM> process, the remaining water in the concrete should not fall below <NUM>% of the initial water content by mass.

The formed optionally reinforced demoulded conditioned slag-based intermediate <NUM> products are then placed in a sealed room, chamber or vessel. Carbon dioxide <NUM> gas is introduced to cure the demoulded conditioned slag-based intermediate <NUM>-at <NUM>%, preferably <NUM>%, preferably <NUM>%, preferably <NUM>%, preferably <NUM>%, preferably <NUM>%, preferably <NUM>%, preferably <NUM>%, preferably <NUM>%, preferably <NUM>%, or preferably <NUM>% purity-into the enclosed area, that may be a chamber/enclosed space/vessel/room at ambient temperature. The gauge pressure of the chamber/enclosed space/vessel/room will gradually increase to a range of <NUM> psi to <NUM> psi.

In a preferred alternative to the curing chamber, the demoulded conditioned slag-based intermediate <NUM> products can be covered and sealed by airtight fabrics. The CO<NUM> <NUM> is then introduced into the space created by these fabrics.

The demoulded conditioned slag-based intermediate <NUM> products are kept pressurized under CO<NUM> gas <NUM> for no less than <NUM> minutes, though the CO<NUM> curing <NUM> process can continue for up to <NUM> hours, where a preferred embodiment is <NUM> hours for CO<NUM> curing <NUM>. The chamber/enclosed space/vessel/room's internal temperature will gradually increase by at least <NUM> before it decreases as a result of an exothermic, accelerated curing reaction-the "CO<NUM> activation process". At the end of the activation process, the remaining CO<NUM>, if any, is vented out.

The following are preferred examples for <NUM> cubic meter (m<NUM>) of the wet-cast slag-based concrete <NUM> described herein having the following the non-zero-slump concrete properties :.

The present method is not limited to the operable/preferred compositions presented above. Furthermore, if water reducing admixtures (i.e. chemical admixtures <NUM>) are included in the non-zero-slump concrete <NUM>, lower water contents (lower water to binder ratio) may be required.

<FIG> schematically represents the step of casting <NUM> the mixed non-zero-slump concrete <NUM>, into an appropriate mould where at least partial setting occurs. The steps of de-moulding <NUM> and pre-conditioning <NUM> are represented by one arrow and the CO<NUM> curing <NUM> of the demoulded conditioned slag-based intermediate <NUM> occurs in a preferred embodiment in a CO<NUM> curing chamber. In a preferred embodiment pre-conditioning <NUM> of the demoulded intermediate <NUM> may also occur in the curing chamber with air rather than CO<NUM> being used, then followed by the CO<NUM> curing <NUM>.

Claim 1:
A method of producing a wet-cast slag-based concrete product comprising steps of:
providing a slag-based binder, an aggregate and water;
mixing the slag-based binder, the aggregate and the water to produce a non-zero-slump concrete composition comprising a first water to slag-based binder ratio by weight of greater than <NUM>;
casting the non-zero-slump concrete composition by transferring the non-zero-slump concrete composition into a mould;
setting the non-zero-slump concrete composition within the mould to produce a slag-based intermediate comprising a second water to slag-based binder ratio by weight that is less than the first water to slag-based binder ratio by weight;
demoulding the slag-based intermediate to produce a demoulded intermediate;
pre-conditioning the demoulded intermediate to produce a demoulded pre-conditioned slag-based intermediate comprising a third water to slag-based binder ratio by weight that is less than the first water to slag-based binder ratio by weight and that is also less than the second water to slag-based binder ratio by weight; and
curing the demoulded pre-conditioned slag-based intermediate with carbon dioxide to produce the wet-cast slag-based concrete product,
wherein
the step of casting of the non-zero-slump concrete composition is free of pressing/compaction.