GB2609887A - Concrete washout materials and system - Google Patents

Abstract

Concrete washout materials are disclosed, wherein the materials are a composite material in the form of a liner for a concrete washout containment sack, or a composite material in the form of a concrete washout containment sack. The composite material may comprise a porous material that comprises at least one powder form pH adjusting material coated onto one or more exterior surfaces of the porous material. Alternatively, the composite material may comprise a porous material that comprises at least one pH adjusting material impregnated into the porous material. In a further aspect, a concrete washout containment sack comprises one or more composite pH adjusting materials. In the latter aspect, the composite material may be a liner fitted into the interior of a containment sack, and which may be bonded or secured to the containment sack. A method of concrete washout treatment comprises passing cementitious wash water into a containment comprising the composite material, collecting the cementitious material within the containment and allowing wash water to exit the containment through the composite material to adjust the pH of water retained within the containment to a pH of 10 or less by the dosing of pH adjusting material from the composite material.

Description

CONCRETE WASHOUT MATERIALS AND SYSTEM

[0001] This invention relates to a cementitious washout system and to materials and to devices incorporating such materials for use in such systems.

[0002] Hereinafter reference to concrete is a reference to cementibous materials in the form of concrete or other cement containing compositions. Concrete mixers, wagons and related equipment need to be washed off regularly and this creates concrete wash waters. Managing the disposal of concrete wash waters legally and in an environmentally responsible way has always been difficult for the construction industry and now it has a raised profile and concern to regulators. Concrete Washout Treatment Systems have therefore been developed to safely reduce the pH of the contaminated wash water. Wash water may be used to remove concrete in the uncured state or the green state, which is a condition where the concrete is not fully cured, from equipment used in the manufacture and or use of concrete. Water in contact with uncured concrete residues and/or green concrete will have a raised pH well above pH 7. Concrete wash waters are therefore potentially both hazardous and polluting and typically they have a high pH (11-13), high suspended solids and other trace materials, some originating from cement, others from additives or from the mixing equipment. When water is used to wash the chute on a concrete wagon, for example, the water is in contact with the concrete for a very short time. The pH of this water will hardly be raised at all. However, if both the water and the concrete are washed into a skip the water will remain in contact with the concrete and its pH will rise to typical values of 12 and above. This is enough to present significant CoSHH issues as the wash water can cause burns to skin and damage eyes on contact. The water will often appear clean and if left in a skip may even appear inviting to a child to swim in. It is this water with raised pH that is the serious pollutant in these scenarios and not the solids from the concrete. The pH of the water continues to rise when it is in contact with green concrete. Once the concrete has cured it is safe. Water rarely evaporates from containment skips or bunds it must either be treated prior to discharge or disposed of according to current legislation by a licensed contractor with a documented waste trail. Failure to do this would indicate deliberate release to the environment, which is an offence.

[0003] A commercial Concrete Washout Treatment System is provided by Mudtech Limited. This system is based on the use of a pH adjusting additive in combination with an appropriate filtration and water re-use system, which incorporates a sack collector. This system is based on reducing the time wash water is in contact with cement, the removal of solids from standing water as soon as possible, recycle of water in order to reduce water consumption and wastewater disposal, maintenance of wastewater pH to below 10 to reduce the risk of harm to workforce, the public and the environment, and reuse of cured solids as hardcore or disposal as non-hazardous concrete waste. The wastewater is separated from the concrete washout in a sack collector and treated with pH adjusting additive in the system. The adjusted (pH below 10) wash water may be accepted by most sewage undertakers.

[0004] In JP2006102705A there is described a draining sheet equipped with a citric acid powder and a pair of spun-bond nonwoven fabric for holding and supporting the powder. This sheet is used flat to treat wash water containing cured cement residues from the sandblasting (and similar methods) of cured cement structures during construction processes or cleaning operations, [0005] A recent development are self-dosing sacks as provided by Mudtech Tank Division Limited under the brand BlueRinse that consist of solid particulate pH adjusting material that is trapped between two bonded porous materials. The porous materials are bonded to each other through the use of needle punching, trapping the solid pH adjusting material between them. Whilst highly effective these sacks are difficult to manufacture and to provide maximum control over pH additive levels.

[0006] Despite the systems for concrete washout known in the art there is a continuing need for alternative and/or more effective solutions for concrete washout systems in general and for new materials and devices for use in such systems. There is a specific need for improved and more effective materials for pH dosing and control.

[0007] The present invention is directed to a modified and improved concrete washout system and in particular the washout from the cleaning of equipment used in the manufacture of concrete that may be contaminated with uncured concrete residue and or green concrete. The new system utilizes a composite material in the form of a liner for or as an integral part of a concrete washout containment sack. Thus, the composite material may be in the form of a removable liner which may be fitted within the interior of a containment sack or as a liner which may be fitted into the interior of a containment sack, and which is bonded or secured by some means to the containment sack or may comprise the wall of a sack from which it is at least in part manufactured.

[0008] The composite material provides adjustment to the pH of concrete washout through the controlled dosing of pH adjusting material to the wash water used for concrete washout, that has been temporarily retained within a concrete washout containment sack, as it passes from that containment sack and through the composite material comprising pH adjusting material.

[0009] The composite material of the present invention comprises a pH adjusting material integrated into a porous support material to form the composite. The composite material in some embodiments may be easier to manufacture than known systems and/or may provide more flexibility for the development and design of effective concrete washout systems.

[0010] The composite material of the present invention in a first embodiment comprises a porous material that comprises at least one pH adjusting material deposited upon one or more external surfaces of the porous material. In this embodiment the pH adjusting material may be deposited via a number of techniques with the pH adjusting material in liquid form (solution) or in a highly dispersed form. These techniques include spraying, liquid coating, or printing techniques. They are characterized by the evaporation of a liquid vehicle that leaves the pH adjusting material as a layer of material bonded to the surface of the porous material or as fine but discrete particles of material bonded to the surface of the porous material. By the nature of these deposition techniques there may be some penetration into the porous material from the deposition surface, but the deposited pH adjusting material is primarily deposited on one or more surfaces. When on a single or two surfaces the composite has an asymmetric distribution of pH adjusting material in the final composite with the interior and for single surface deposition the bulk of the porous material being devoid of pH adjusting material.

[0011] The composite material of the present invention in a second embodiment comprises a porous material that comprises at least one pH adjusting material impregnated into the porous material. In this embodiment the pH adjusting material may be impregnated using one or more techniques such as liquid impregnation, melt impregnation or solid powder impregnation. Which techniques is used will depend on the form of the pH adjusting material, which may be used as prepared or dispersed/dissolved in a liquid carrier or a polymeric or other organic carrier such as a wax of similar material. The level of impregnation may be controlled to provide a symmetric homogeneous dispersion of pH adjusting material throughout the porous material or may be controlled to provide only partial impregnation thus providing an asymmetrical composite material.

[0012] The composite material of the present invention in a third embodiment comprises a porous material that comprises at least one powder form pH adjusting material powder coated onto one or more exterior surfaces of the porous material. In this embodiment various powder coating techniques may be used to provide the surface coating of the pH adjusting material, which may be in powder form as manufacture or may be dispersed in a matrix to provide a powder form suitable for powder coating techniques.

[0013] In each of the first to third embodiments the composite material may further comprise a structure that consists of at least three components wherein at least one of the components is a region which comprises additional pH adjusting material and wherein this region of additional pH material is secured within the composite between a first and second layer of the porous material bonded to one other and preferably mechanically bonded through the region of additional pH adjusting material. In this arrangement with reference to the first embodiment pH adjusting material is also deposited upon one or more of the external surfaces of the porous material. In this arrangement with reference to the second embodiment pH materials is also deposited via impregnation within one or both of the porous layers. In this arrangement with reference to the third embodiment powder form pH materials may be powder coated onto one or more external surfaces of the porous material.

[0014] It is also envisaged within the invention that the first, second and third embodiments may be combined in any binary combination thereof or all three may be combined to provide a composite material in the form of containment sack or liner for a containment sack.

[0015] With reference to the structure comprisng three components the bonding may be adhesive bonding, thermal bonding or solvent bonding and preferably is mechanical bonding. Mechanical bonding between these adjacent layers may be achieved through use of one or more of the following mechanical bonding techniques; needle punching, or stitch bonding. It is preferred that the adjacent layers are mechanically bonded to each other via needle punching. Mechanical bonding is distinct from adhesive bonding, which is preferabiy avoided for bonding the porous layers adjacent to the pH adjusting material layer to each other although these porous layers individually may comprise adhesively bonded material. Mechanical bonding requires the interlocking of material from and between the adjacent porous material layers and/or the use of a third material in the form of for example a thread or staple mechanically securing the adjacent porous layers to each other. It is preferred that the mechanical bonding is as a result of the interlocking of material from and between the adjacent porous layers.

It is possible to use one or more of these mechanical bonding techniques in combination with flame lamination of the layers, however it is preferred that the composite of the present invention is manufactured without the use of flame lamination.

[0016] The porous materials used in the composites of the present invention may comprise woven and/or non-woven materials and preferably comprise non-woven materials. Preferably these layers are non-woven fibrousiay:.',rs that are hydrophilic and porous enough so that water may pass therethrough. Also envisaged are spun bond or other material types that are sufficiently porous and which may support sufficient Ph adjusting material.

[0017] The porous non-woven layer materials may be broadly defined as sheet or web structures. They are flat or tufted porous sheets that are made directly from separate fibers, molten plastic or plastic film. They are not made by weaving or knitting and do not require converting the fibers to yarn.

[0018] These nonwovens are typically manufactured by putting small fibers together in the form of a sheet or web and then binding them either mechanically (as in the case of felt, by interlocking them with serrated needles such that the inter-fiber friction results in a stronger fabric), via adhesive, or thermally often with use of a binder material.

Examples of suitable non-woven materials include staple nonwovens, melt-blown nonwovens, spun laid nonwovens, flash spun, spun jet, air-laid, wet-laid and other well-known forms. In many of these forms the laid fibre requires further treatment in the form of bonding of fibres to provide physical integrity to the nonwoven layer. Several bonding methods may be used and include be used: thermal bonding, hydro-entanglement, ultrasonic pattern bonding, needle punching/needle felting, chemical bonding with binders and melt-blown, where fiber is bonded as air attenuated fibers intertangle with themselves during simultaneous fiber and web formation.

[0019] When porous materials are used as bonded layers sandwiching a pH adjusting material between them each of the nonwoven layers may be of the same material and form or may be made of different materials and/or forms. Thus, in one example the composite may comprise a layer of needle punched material such as polyester and the other layer may for example be a spun bond polyester. In a preferred embodiment the spun bond layer is arranged to be proximate to the surface from which treated wash water will exit the composite during use. In the case of a sack for collecting concrete waste the spun bond surface of the composite will sit adjacent the inner surface of the sack when the composite is used as a liner or permanently secured to the sack. The nonwoven needle punched layer is located at the internal surface of the composite facing the interior of the collection sack. It is this layer, which first comes into contact with concrete wash water as it enters the sack which is lined with the composite of the preset invention. During use the concrete wash water enters the lined sack and on passing through the composite liner or wall all fines are filtered by the nonwoven layer. High pH water then passes through the pH adjusting material layer and its pH is reduced before the pH adjusted water passes through the spun bond layer and out of the sack walls.

Thus, in use the composite liner removes concrete fines from the high pH water and adjusts the pH before the pH adjusted wash water is then passed to drainage facilities on site or collected for later disposal.

[0020] Although the first second and third embodiments may comprise a single layer of porous material it also envisaged that they may have a multi-layered porous material. In this arrangement one preferred option is for the porous material of the composite in contact with the interior of the bag is a spun bond and this is attached to a porous material of needle punched polyester or similar with its exposed surface facing inwards to the interior of the collection sack. In this arrangement the pH adjusting material may be exclusively associated with the spun bond layer in the forms provided by embodiments one, two or three and the needle punched or similar nonwoven proximate to the interior of the collection bag is free of pH adjusting material and only acts as a filter of fines from the concrete wash water as it passes through the composite materials of the invention for pH adjustment via dosing with pH adjusting material from the spun bond layer. The composite materials of the present invention have two key functions; the primary function is to dose pH adjusting material into concrete wash water to reduce pH and the second is to act as a filter for fines that may be present in the wash water.

[0021] One suitable nonwoven is a hydrophilic polyester needle punched felt material typically of 550 g per square meter and of a thickness of approximately 4 mm.

Polypropylene or other polyolefin based felt materials. The fibres are needled to form a stable network that retains dimensional stability relative to each other. One preferred nonwoven material for one or more of the layers is a spun bond felt. The preference is for materials that have the desired level of hydrophilic properties, which allow the wash water to pass through the composite.

[0022] The pH adjusting material may be any material that may be dissolved in and/or interact with water or basic solutions and which is capable of adjusting the pH of a high pH solution of pH 11 or greater to lower the pH, preferably to a pH of 10 or less.

Examples of such materials include sodium bicarbonate, citric acid, citrates, or similar materials. The preferred pH adjusting materials are non-acidic materials so that at any dosing level the resultant pH adjusted wash water is not rendered acidic. The preferred materials are in powder or gel form and are materials that are capable of adjusting solution pH from highly alkaline levels of pH 11 or greater to levels of pH 10 or less.

The preferred materials are bicarbonates and preferably sodium bicarbonate in powder or gel form. The pH adjusting material may be formulated with and dispersed in a matrix such as a water swellable or dispersible polymer matrix.

[0023] The composite materials of the present invention may be in the form of a liner, which comprises a mat bottom and upstanding sidewalls of the same material.

This liner may be located within a flexible intermediate bulk container (FIBC) or a vented bulk building materials bag or sack. The composite liner may be removable and replaceable or may be permanently secured to the sack walls via stitching or other suitable methods. The composite material of the present invention may be in the form of a replaceable mat or a fixed mat for a containment. As a liner it may be of any suitable size depending on the size of the bag or sack used for the washout system; the bag may be designed for single or multiple concrete washout cycles.

[0024] With reference to the structure comprising three components the preferred method of manufacture of the composite material of the present invention is to distribute powder or gel form pH adjusting material at the desired level of loading as a layer onto a web of a desired fibrous non-woven material and then to locate a second web of the nonwoven on top of the layer of pH adjusting material. This loose multilayered composite is then introduced into a needle punching machine at the desired settings to needle punch the two nonwoven layers together trapping and securing the powder form material between them to form the composite. Preferably the nonwoven materials of density of from 50 to 700 g per square meter, more preferably density of from 50 to 600g per square meter and preferably 70 to 550g per square meter. Located and sandwiched between these nonwoven layers is between 500g - 1000g per square meter of pH adjusting material. In one embodiment both of the nonwoven layers are needle punched polyester. In a further embodiment the composite comprises one needle punched polyester layer and the second layer is a spun bond layer, preferably spun bond polyester. When present it is preferred that the spun bond layer has a density of from 50 to 150g per square meter, more preferably 50 to 100g per square meter and most preferably from 50 to 80g per square meter and ideally about 70g square meter.

[0025] The composite materials of all embodiments of the invention may typically contain between 500g -1000g per square meter of pH adjusting material. It is envisaged that different levels of pH adjusting material may be achieved depending on which embodiment or combination of embodiments are selected to provide the final composite material. For example, a certain level of pH adjusting material may be imparted to the surface of the composite material as provided by the first embodiment after a significant level of pH adjusting material has been impregnated into the porous material as indicated in the second embodiment. It is envisaged therefore that the use of one or two or more of the first to third embodiments optionally with sandwiched pH adjusting material provides for a wide level of control and optimization of the level of pH adjusting material within the final composite material and furthermore provides high levels of optimization of the location of the pH adjusting material within the composite material and within the containment sack. This flexibility enables the design of concrete wash out systems that are maximized for efficiency and efficacy when in use.

[0026] It is understood that any embodiment described herein may be used in combination with one or more of each of the other embodiments and all of these combinations of embodiments are within the scope of the present invention.

[0027] All of the features disclosed in this specification for each and every embodiment (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Claims (9)

1. CLAIMS1. A concrete washout composite material in the form of a liner for a concrete washout containment sack.
2. 2. A concrete washout composite material in the form of a concrete washout containment sack.
3. 3. A concrete washout containment sack comprising one or more composite pH adjusting material.
4. 4. A concrete washout containment sack according to claim 3, comprising the composite material in the form of a removable liner which may be fitted within the interior of a containment sack.
5. 5. A concrete washout containment sack according to claim 3, comprising the composite material may be in the form of a liner which is fitted into the interior of a containment sack, and which is bonded or secured by some means to the containment sack.
6. 6. A concrete washout composite material as claimed in claim 1 or 2, wherein the composite material comprises a porous material that comprises at least one pH adjusting material deposited upon one or more external surfaces of the porous material.
7. 7. A concrete washout composite material as claimed in claim 1 or 2, wherein the composite material comprises a porous material that comprises at least one pH adjusting material impregnated into the porous material.
8. 8. A concrete washout composite material as claimed in claim 1 or 2, wherein the composite material comprises a porous material that comprises at least one powder form pH adjusting material powder coated onto one or more exterior surfaces of the porous material.
9. 9. A method of concrete washout treatment, comprising passing cementitious wash water into a containment comprising a composite a concrete washout composite material according to any one of claims 1 to 8, allowing the cementitious material to be collected within the containment for disposal and allowing wash water to exit from the containment through the composite material such that the pH of any water or wet cementitious material retained within the containment is adjusted to a pH of 10 or less by the dosing of pH adjusting material from the composite material.