AU778765B2 - Modified concrete transport mixers - Google Patents

Description

.4 -1- P/00/0011 Regulation 3.2

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

Name of Applicant: Actual Inventor: Address for service in Australia: Invention Title: MBT HOLDING AG Robert Alfred MARKS, Paul William HEIS, Anthony Francis

COOPER

Freehills Carter Smith Beadle 101 Collins Street Melbourne Victoria 3000 Australia MODIFIED CONCRETE TRANSPORT MIXERS Details ofAssociated Provisional Application: PQ4417 filed 2 December 1999 The following statement is a full description of this invention, including the best method of performing it known to us -2- Field of the Invention This invention relates to concrete transport mixers that include a rotary storage container, and in particular to modified concrete transport mixers adapted to allow the addition of admixtures to the rotary storage container. The invention also provides a method of adding an admixture to the rotary storage container of a concrete transport mixer.

Background of the Invention Concrete is a widely used construction material. It is usually prepared by mixing coarse aggregates such as rock or stone screenings; fine aggregates such as sand; hydraulic cement and water to form a pourable plastic mixture. This mixture is then usually poured to form the shape of the desired final material. After pouring, well known curing mechanisms that involve hydration take place and the plastic mixture is converted to a solid material. This cured solid material may be used for structural as well as decorative purposes.

Concrete is usually transported by trucks to the site where the concrete is to be placed and cured. The trucks typically have a rotary storage container that is rotatable by a drive mechanism to allow mixing of the concrete while it is being transported. The ingredients that are to form the concrete are usually added to the 20 truck's rotary storage container at a central depot. At some depots the concrete ingredients are premixed before they are added to the truck's rotary storage container. Mixing of the ingredients is carried out by slow rotation of the rotary ooeo• storage container about its longitudinal axis. A vane or baffle is located on the inner wall of the rotary storage container and this may facilitate the mixing of the concrete within the container. The vane is usually in the form of a continuous coil like spiral. When the concrete is to be discharged from the rotary storage container the direction of rotation of the rotary storage container is reversed. This causes concrete to be continuously fed between the flutes of the spiral vane to a discharge opening and chute located at the rear of the rotary storage container. This 40467838:CAP.DVG:JMD 30 November 200011:29 -3arrangement of the spiral vane permits the concrete to be discharged at a rate dependent on the speed of rotation of the rotary storage container.

As known in the art, an admixture is a material other than hydraulic cement, water and aggregates that is used as a concrete ingredient. It is usually added to the concrete batch immediately before or during its mixing. Admixtures are well known and their properties and applications are set out in standard texts such as "Concrete Admixtures Handbook" 2 nd Edition) edited by V.S. Ramachrandron (Noyes Publications) Admixtures are used to modify the properties of the concrete in such a way as to make it more suitable for a particular purpose or for economy. The major reasons for using admixtures are: 1. to achieve certain properties in concrete more effectively than by other means; 2. to maintain the quality of concrete through the successive stages of mixing, transporting, placing, and curing during adverse weather or traffic conditions.

3. to reduce the cost of concrete construction.

For example, use of an admixture may allow less expensive construction S2. methods or designs to be utilised thereby offsetting the costs of the admixture.

Admixtures may also allow environment benefits. For example, at the end of a day's delivery, the rotary storage container may contain residual cement, sand or aggregate. When left in the container overnight, the residual concrete will settle and harden in the bottom of the container. To prevent this occurring, the residual materials can be washed out of the container with water. However, this can be wasteful of the unused concrete and also lead to disposal problems that are potentially damaging to the environment. A potential solution to this problem is to add an admixture known as a retarder to the residual concrete in the storage container. This retarder slows the cure of the concrete sufficiently to enable the residual concrete ingredients to be incorporated with the next day's mixture.

A commonly used admixture is a plasticiser or superplasticiser. These admixtures are used to adjust the rheology of the plastic concrete mix to allow the 40467838:CAP.DVG:JMD 30 November 200011:29 -4convenient use of pumps as well as the attainment of the desired level of slump at the specified final compressive structural strength. These admixtures are typically used at levels of from 1 to 5 litres per cubic metre of concrete. To reduce the viscosity of the concrete mix, water is often added to the mix at the placing site. Water is normally added from a reservoir on the truck, as the availability of water at the placing site is unreliable. However, the addition of excessive amounts of water may have severe consequences in reducing the ultimate structural strength of the cured concrete. The ultimate strength of cured concrete is dependent on the amount of water in the concrete mix. The use of plasticisers and superplasticisers is a well known method of adjusting the rheology of the wet concrete mix without detracting from its ultimate structural strength.

Admixtures are usually added to a concrete batch at the central depot at about the same time as the other concrete ingredients. In practice it is common for at least an hour to elapse before the wet concrete mix is transplanted to and placed at the forming 15 site. Over this time the effect of certain admixtures may change and sometimes the same benefits as were initially available are no longer available. For example, with plasticisers and superplasticisers, the initial beneficial lower viscosity may be no longer available. It is believed this change in rheology is a consequence of the physical and chemical reactions that are taking place over time between the concrete ingredients and the plasticisers or superplasticisers. A further difficulty with adding admixtures at the central depot is that it is often difficult to predict when the concrete will be poured and o. the weather conditions at that time. For example, it is not uncommon for delays to occur either through transport difficulties or delays on the construction site.

Accordingly, it is difficult to add the optimum type or amount of admixture at the depot.

25 It is therefore desirable to be able to add admixtures at the placing site. One method used to achieve this is to have an additional transport vehicle that has reservoirs of admixtures and which can be despatched to the placing site to be available to add admixtures, if required, when the concrete transport mixers arrive. However, such methods are labour intensive and expensive and are only used on large construction sites where the additional expense can be justified.

03/09/04,at I 3223.specipgs,4 Summary of the Invention This invention provides in one form a concrete transport mixer that mixes during transport, the mixer having a rotary storage container adapted to discharge concrete through a discharge opening, and having a water storage vessel, wherein the concrete transport mixer further includes an admixture storage vessel for storing a liquid admixture; the admixture storage vessel having an inlet to allow liquid admixture to be added to the admixture storage vessel and an outlet that is connected via a conduit to a discharge point located at the discharge opening of the rotary storage container, injecting means for injecting the admixture from the admixture storage container to the rotary container; and regulating means to allow desired amounts of admixture to be added to the rotary container; and S 15 wherein the injection means is adapted to inject the admixture to the distal end o of the rotary container.

Preferably the injecting means includes a means for maintaining pressurised gas above the liquid admixture in the admixture storage vessel.

SPreferably the pressurised gas is maintained at a pressure of between 0.14 and 20 0.52 MPa.

Preferably the admixture storage vessel includes a number of compartments for separately storing a number of liquid admixtures.

In an alternative form this invention provides a method of adding admixtures to ooso a rotary storage container of a concrete transport mixer comprising injecting at least one 25 admixture from a storage vessel located on the concrete transport mixer by actuating a control valve that allows admixture to be injected under pressure to the rotary container, monitoring the amount of admixture that is added and actuating the control valve to stop the addition of admixture to the rotary container when the desired amount of admixture has been added.

The invention will be further described by reference to a preferred embodiment illustrated in the accompanying drawing.

03/09/04.at 1 3223. -6- Brief Description of the Drawing Figure 1 is a schematic drawing of a modified concrete transport mixer.

Detailed Description of the Invention Referring to Figure 1, the modified concrete mixer 1 consists of a rotary storage container 2 with drive mechanism 3 to allow reversible slow rotation of the rotary storage container 2. A discharge opening 4 is located at the end of the rotary storage container 2. An admixture storage vessel 5 of capacity 30 litres is fabricated from stainless steel to a design strength sufficient to withstand pressures up to 150 psi. Liquid admixture is added to the storage vessel 5 by inlet 6 via a one way valve. The storage vessel 5 is pressurised by compressed air fed into the storage vessel 5 via a second inlet 7 from a source used by the truck to supply compressed air to its brakes. The pressure of air in the storage vessel 5 is maintained at about psi. However, other pressure can be used. These can range up to 125 psi that is S usually available from a truck for its brakes. Pressures of above about 50 psi are not 15 preferred as otherwise more robust flow meters are required. If the pressure is too .ooo.: S•low the admixture is not injected far enough into the rotary storage container.

The storage vessel 5 has an outlet 8 which is connected via a pressure hose conduit to a 10mm diameter copper pipe outlet 9 located in the discharge opening 4.

Located before the outlet is a flow meter 10 and hand actuated control valve 11.

In use, a plasticiser is added to the storage vessel 5 via inlet 6. A pressure of approximately 40 psi is maintained via the second inlet 7 and controlled at that pressure using a control valve. Plasticiser from the storage vessel is injected into the rotary container 2 in response to actuating the control valve The plasticiser is injected to the distal end of the rotary storage container 2.

When the desired amount of plasticiser has been injected as determined by the flow meter the control valve is turned off. Addition of the plasticiser to the distal end of the rotary storage container leads to more rapid incorporation of the admixture into the concrete batch. Injection to or near the distal end of the rotary storage container is a particularly beneficial feature when the admixture is a plasticiser or superplasticiser.

40467838:CAP.DVG:JMD 30 November 200011:29 -7- A number of variations from the preferred embodiments can be made. For example, while it is convenient to use the pressurised air that is normally available in a truck to inject the plasticiser, other injection means may be used. For example, a mechanically driven or electrically driven pump may be used. A further variation is to have multiple compartments in the storage vessel that could store different admixtures. These could be fed by separate conduits to outlets located at the discharge opening of the rotary storage container. Alternatively, separate storage vessels could be used for each admixture. Two admixtures that would be of particular advantage would be a retarder and either a plasticiser or a superplasticiser. The capacity of the storage vessel used may be varied. Generally the capacity needs to be at least sufficient to hold as much admixture as might be required in one concrete batch.

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Claims (6)

1. A concrete transport mixer that mixes during transport, the mixer having a rotary storage container adapted to discharge concrete through a discharge opening, and having a water storage vessel, wherein the concrete transport mixer further includes an admixture storage vessel for storing a liquid admixture; the admixture storage vessel having an inlet to allow liquid admixture to be added to the admixture storage vessel and an outlet that is connected via a conduit to a discharge point located at the discharge opening of the rotary storage container, injecting means for injecting the admixture from the admixture storage container to the rotary container; and regulating means to allow desired amounts of admixture to be added to the rotary container; and wherein the injection means is adapted to inject the admixture to the distal end of the rotary container.

2. A concrete transport mixer as defined in claim 1 wherein the injecting means includes a means for maintaining pressurized gas above the liquid admixture in the l1 Soadmixture storage vessel. 20

3. A concrete transport mixer as defined in claim 2 wherein the pressurized gas is maintained at a pressure of between 0.14 and 0.52 MPa.

4. A concrete transport mixer as defined in any one of claims 1 to 3 wherein the admixture storage vessel includes a number of compartments for separately storing a 25 number of liquid admixtures.

5. A method of adding admixtures to a concrete transport mixer that mixes during transport, the mixer having a rotary storage container adapted to discharge concrete through a discharge opening, comprising injecting at least one admixture from a storage vessel located on the concrete transport mixer by actuating a control valve that allows admixture to be injected under pressure to the rotary storage container, monitoring the amount of admixture that is added and actuating the control valve to stop the addition of admixture to the rotary container when the desired amount of admixture has been added and wherein the admixture is injected to the distal end of the rotary storage container. 26/I 0104.at 13223.claims,8

6. A concrete transport mixer substantially as hereinbefore described with reference to the drawing. DATED this 26h" day of October, 2004 MIBT HOLDING AG By their Patent Attorneys: CA= LWE 26/10/04,at I 3223.clainms,9