Measuring and testing – Liquid analysis or analysis of the suspension of solids in a... – Content or effect of a constituent of a liquid mixture
Patent
1997-11-12
1999-09-28
Brock, Michael
Measuring and testing
Liquid analysis or analysis of the suspension of solids in a...
Content or effect of a constituent of a liquid mixture
374 45, 366 17, 73 6171, G01N 2500, G01N 1506, B28C 704
Patent
active
059591978
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a method for determining or estimating the free or available cement content in concrete plant waste water and to a system for performing the method to provide a measurement of the free cement content of a particular body of waste water.
BACKGROUND OF THE INVENTION
In our Australian Patent Application No 10247/92, we have described a system for recycling concrete plant waste water. The system consists of a central. high pressure pump which draws in the polluted water through a series of devices, where atmospheric air is injected into it. The aerated water is then returned to the pit via jet nozzles located around the floor. The thrust produced by these nozzles rotates the water around the pit, the movement resulting in the encapsulation of the semi-hydrated cement particles in the air bubbles. By the principle of buoyancy, these particles expand and rise towards the surface, the rotating water naturally vectoring them towards the central pump. This allows for their recirculation through the system, or their diversion through the batching water system, and subsequent re-use in concrete production. Water from the agitator pit is also used to wash out truck agitator barrels, this cement rich water then being returned to the agitator pit via an aggregate and sand collector box.
The amount of cement present in the pit at any one time bears no relation to it's volume in weight, but depends on what is termed the "activity factor". For example, after a weekend of no plant production, the pit would have a very low activity ratio, that is more cement particles in relation to volume of water.
Accordingly, to maximise the benefits from the agitation system described above, a method of measuring the free cement content of a particular volume of waste water would be most beneficial.
SUMMARY OF INVENTION AND OBJECTION
It is the object of the present invention to provide a method of determining or estimating the free cement content of concrete plant waste water in a simple but accurate manner which in turn allows the determination of the reduced amount of cement possible in a particular batch using the waste water while still producing a full strength concrete product.
The invention therefore provides a method of determining the free cement content of concrete plant waste water, comprising holding the waste water in a pit or tank, agitating the waste water to keep the solids in the waste water substantially in suspension, measuring the temperature of the waste water in said pit, measuring the temperature of water in a reference pit or tank, determining the difference in the measured temperatures, and using the temperature difference to calculate an estimate of the free cement in said waste water.
It has been found that the amount of cement saved R in kilograms is able to be calculated according to the following formula: ##EQU1## in which V is the volume of waste water under consideration, .DELTA.T is the temperature difference referred to above and V is the volume of water in each concrete batch in liters per meter.sup.2 of concrete.
If desired, an allowance is made for the temperature rise in the agitated pit due to the pumping activity and this value for a particular pit and pump combination is subtracted from the temperature difference in the above formula. The modified formula reads: ##EQU2##
By determining the amount of free cement in the waste water, the amount of cement used in a batch of concrete prepared using part or all of the waste water can be correspondingly reduced in an accurate manner whereby the strength of the concrete product is not compromised while cost savings are still achieved.
The water in the reference pit may be clean water or polluted water but should not contain significant amounts of cementitious material, otherwise its ability to provide a proper reference will be somewhat compromised.
In another aspect, the invention provides a system for determining the free cement content of concrete plant waste water, comprising a waste water pit or
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patent: 4192745 (1980-03-01), Hood
patent: 4488815 (1984-12-01), Black
patent: 4588299 (1986-05-01), Brown et al.
patent: 4715726 (1987-12-01), Tsuruta
patent: 5209130 (1993-05-01), Ohsaki et al.
patent: 5685978 (1997-11-01), Petrick et al.
Brock Michael
Politzer Jay L.
Thermo Crete Pty Ltd
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