subject: Concrete Waste Water Management [print this page] The disposal of waste water from ready mixed concrete (RMC) procedures and on construction sites has been of fantastic concern not merely amongst the regulators and also the public but also with all the ready-mixed concrete producers. These days, the traditional disposal system is no longer allowed and is deemed environmentally un-friendly.
It's a recognized fact that several ready-mixed concrete plants (such as concrete transporting trucks) completely clean the concrete mixer and truck drums on each day following the operation. Practically 150-300 gallons of water are required for cleaning such a facility and later such concrete waste water is discharged or disposed. In accordance with the Water High quality Act (1987) in USA, concrete waste water is hazardous which comprises of caustic soda and potash. Therefore, the disposal of concrete waste water is subject to stringent regulatory requirements from the Environmental Protection Agency (EPA).
Besides above, the high pH value of concrete waste water is considered highly corrosive according to EPA standards. Also, because of its high alkalinity, when discharged to natural water courses or streams, it may burn and kill fish, insects and plants. As an example, concrete waste water has a pH value between12-13 in comparison with pH value of freshwater (6-7). Therefore, it is highly toxic comparable to household bleach as well as other domestic cleaners. A small amount of concrete waste water can simply kill hundreds of fish.
The actual current techniques employed for disposal of concrete waste water consist of dumping in the construction web site, disposal at a land fill, storm-water drain or natural stream, or dumping into the wash pit in the ready-mix batching plant. The management and disposal of concrete waste water has been further affected because of a lack of disposal and land fill web sites obtainable. Because of this, numerous ready-mix operators have commenced their own disposal strategies to manage such waste water.
The particular option disposal methods used by the ready-mix plant operators include storm water detention or retention facilities, settling tanks and water recycling systems. In accordance with available statistics, any RMC plant getting a production capacity around 250m3/day could generate 1000 litres of waste water. The volumes involved are so huge, so appropriate disposal procedures and management is vital for long term environmental sustainability.
Hence, one of the most desirable techniques of managing waste water is always to recycle waste water that could minimize waste water volumes appreciably. It is important for anybody involved in RMC waste water management to particularly appear in to the following elements:
The sources of waste water generation as well as the estimates
The quality or the degree of toxicity of waste water created
Ways to manage waste water
The possibility of using (recycling) of waste water made for production of concrete
The use of chemical stabilisation for concrete manufacture
Reasons for Concrete Waste Water Generation
Concrete waste water is usually gained from the RMC batching plants, the washing of truck mixers, the washing from the batching plant, rain or storm water run-off from the RMC plants, the washing of conveyor belts of RMCs, etc.
When looking at the above sources, it is extremely difficult to accurately estimate concrete waste water generated from these sources, because of the varying nature of water usage. Similarly, the waste water generated from storm water runoff can differ substantially due to altering rainwater intensity.
It is also noted that roughly 300 Kg of concrete gets stuck inside the drum from the RMC truck mixer which features a capacity of 10 cubic meters. Since, a RMC truck mixer has to become cleaned or washed (after finishing concrete) each day, approximately 750 to 1500 litres of water is necessary to clean a single truck of this size. In essence, a typical truck washing facility can create 15,000 to 25,000 litres of concrete waste per day. In such a scenario, considering numerous quantity of RMC plants situated inside a country like USA, we can envision trillion litres of concrete waste water made inside a given day. This is a severe environmental concern which not just pollutes numerous water bodies in the country but additionally endanger the plants, fish and aquatic resources in the country.
The Top quality and Toxicity of Concrete Waste Water
Whenever one closely looks at the top quality of waste water, they could discover that it consists of toxic cement materials, chemical substances utilized as admixtures and fresh water. Also, the quality or the severity of concrete waste water greatly is dependent upon the sources from which it is created for example storm water run-off from RMCs, detention ponds, and truck mixer washing facilities.
Concrete waste water may have high quantities of dissolved limestone. As such, it has high alkalinity or possibly a high pH worth in between 11 and 12. Additionally, it may have dissolved sulphates, metal hydroxides, calcium chlorides employed in admixtures, oil and grease, other chemical substances derived from admixtures. The chemicals like benzene sulphonic acids, ethanolamine, diathonalomine, formaldehydes, and k-naphthalene sulphonate are widely employed in concrete admixtures. This shows the high levels of toxic chemical compounds present in harmless looking concrete.
Ways to Manage Waste Water
It really is apparent that the usage of high volumes of good high quality water (in the sources of concrete waste water) contributes significantly for high volumes of concrete waste water. By controlling and efficient use of water, the problems connected to disposal of concrete waste water could possibly be considerably decreased. In essence, dumping of concrete waste water at work websites or at RMC plants, or in landfills or in truck wash or settling pits could be lowered considerably.
According to the Clean Water Act (1987) in the USA, disposal of concrete waste water at job web sites and RMC plants has been prohibited. In essence, traditional or economical techniques of disposal of waste water has been entirely illegal in many countries.
Which are the alternatives available these days?
The next options are obtainable for the management of concrete waste water:
Usage of chemical stabilising systems: By using chemical admixtures, it avoids the must remove any concrete waste (or wash) water from the concrete truck and mixer drums. More importantly, such wash water can be re-used for creating a lot more fresh concrete. In essence, it assists to recycle of concrete waste water.
The admixtures utilized in this case, aid to stop the hydration process of the concrete in the drums. In other words, it retards the setting of concrete by placing the cement inside the concrete inside a dormant state to get a couple of hours.
By getting such admixtures, disposal of concrete waste water (wash water) could be curtailed top to comply with environmental legislature. Similarly, this reduces water consumption considerably while reducing transport, labour and high maintenance costs at RMC plants.
In thinking about the above, one may wonder regarding the suitability of waste water recycling for creating fresh concrete. Essentially the most acceptable criterion would be to accept water (for mixing fresh concrete) that is potable. Similarly, conventional standards say that water needs to be clean without having any impurities or deleterious supplies. Nevertheless, current research have indicated that concrete waste water much less than 8 hours old could be utilized to produce good top quality concrete. At the same time, it is needed to be positive the other constituents inside the stabilised water are inside the permitted levels.
The employment of admixtures is one in the ways of managing waste water.
Furthermore to the above, managing concrete waste water needs excellent practices such as:
Not allowing waste water and slurry entering into a storm water drain or a stream;
Ensuring that all concrete dust is collected in the RMC plant or in the work website; this can avoid such waste becoming left on web site or plant acquiring washed into a storm water method in the course of rain.
Using as tiny water as possible during the wet cutting of concrete elements. Similarly, provide measures to collect all the slurry created from the wet cutting process.
Avoiding concreting in wet weather.
Putting slurry controls in spot before you begin work.
Always checking and implementing suitable measures to manage and deal with the volume of wastewater made. If chemicals are involved, make certain the waste water is treated prior to disposal.
Ensuring that all concrete pumping gear and conveyors are adequately protected to stop drippings or leakages for the roads or the site.
In summing up, managing concrete waste water can be a expert work that requires sound information and expertise. If it's not correctly managed, severe penalties and very high fines will have to be paid by all parties concerned. Consequently, management of concrete waste water can't be ignored anymore. The present motto is - Polluter Pays.
