Real Time Batch Plant Interview Questions and Answers PDF
• Do You Stock Spare And Service Parts?Yes, Utranazz has a dedicated team for all spare and service part enquiries and we endeavour to keep parts for all our equipment in stock for next day delivery (48 hours for international customers).
• How To Accept Delivery Of Readymix?
Lafarge Readymix aims to be right first time, every time, delivering the correct product at the correct time to its customers. Nevertheless, it is important that the customers check delivery tickets carefully before any readymix concrete is discharged. The few minutes spent doing it properly could avoid a timeconsuming, costly problem later. The procedure is particularly relevant on a large site where there can be several concerting gangs expecting deliveries of concrete with different specifications.
Delivery Notes: Check that the delivery note shows the correct quantity and grade of concrete being delivered, together with essential details of the concrete specification required for the particular job. Another important piece of information is the time of batching the load. This will indicate whether the transport time was normal in relation to the distance traveled or whether there has been an excessive delay between dispatch from the batch plant to site.
Time Limits: Establishing a time limit on the acceptance of concrete as workable and suitable for placement is not straightforward. The rate of change in the properties of concrete depends on the mix constituents, including any special additives, the ambient temperature and general weather conditions. At what stage the concrete becomes unusable also depends on the nature of the job. As a result, the acceptance time period could be less than half an hour or more than six hours and the decision on acceptability is based more on experience than on an objective test.
In an attempt to overcome the reliance on operator judgment, some contract specifications lay down a maximum permitted time between batching and discharging. After which the concrete is deemed to be unsuitable. Unfortunately this can often create another problem.
During a pour, a load may be rejected due to the expiry of the arbitrary time limit but, in the time required to organize a replacement load, the pour site may experience a cold joint problem. In this case, the quality of the rejected load may still have been workable and the better solution could have been to accept the load and continue the pour without interruption. Conversely, the situation can arise in hot weather where a contactor finds that a concrete mix has stiffened unacceptably before the specified time period has lapsed.
The delivered mix may still be within the original tolerance limits, but the concrete is either too stiff or too wet and the originally specified workability is no longer valid. In such instances, Lafarge Readymix should be notified and the arrangements made to supply a concrete mix with workability suitable for the new conditions.
Control through Workability: The workability of a mix is generally considered to be the key quality control indicator for production control purposes at the readymix batching plant and also for the on-site placement. Only when workability is satisfactory are the other properties of the concrete also likely to be correct. Each mix is designed to have a specific workability, which impacts on all the main characteristics of a concrete: with the control of workability being largely based on the free water/cement ratio, this influences final strength and durability, the quality of the surface finish and the ease with which the concrete is transported and compacted.
It is therefore essential that the correct level of workability is specified and maintained within the relevant tolerance. SANS method 861 specifies that the acceptable slump is within a tolerance of 25mm or 30% of the target slump.
When monitoring concrete workability as the primary quality control indicator, it is important to realize that the repeatability of the test results are very dependant on using a methodical testing procedure. Results obtained by two different people on the same concrete sample can differ significantly, especially if the correct test procedures are not rigorously followed.
• How To Order Lafarge Readymix Concrete?
Procedure
o Concrete can be ordered telephonically via our central orders department in the various regions
o Place orders at least 24 hours in advance
o Confirm your order by 12h00 the day before delivery
o All account customers must fax an official order number to our Central Orders Department
o Same day orders will be accommodated if our delivery schedule allows it and the available time is suitable for the customer’s needs
o Special concrete mix requirements can be met, subject to the outcome of trials in our labs by our technical team
o When placing orders, customers will be asked about the application as well as the strength of concrete they require
o If help is required to specify the concrete mix design, please contact the local Lafarge Technical Department
After Hours and Weekend Deliveries
o After hours pours should be arranged with the Lafarge District Sales Manager
o After hours pours will incur extra costs
o Requirements for pours on Sundays should be discussed with the Lafarge Districts Sales Manager
o Sunday deliveries will also incur extra costs
Cancellations
o Cancellations for concrete orders must be done by 15h00 at the latest on the day prior to the pour
o Late cancellations will incur extra cost. If the concrete has been loaded before cancellation, the customer
o will be charged for the full load of concrete
Payments
o Orders being paid for in cash will only be confirmed once payment has been received
o Payments by cheque to the value of R5000 and over must be bank guaranteed
o Internet payments must be done at least 48 hours in advance
o Customers should fax the proof of payment through to the Lafarge Central Orders Department at least four working hours before dispatch of the order is required
Part Load Charges: Loads less than 3m3 will attract a part load charge
Pumping
o The Lafarge concrete pumping service needs to be booked one week in advance
o At least 24 hour notice should be given to cancel a pump booking. Cancellation of a pump on the same day will incur a cancellation fee
Quality Control: Lafarge Technical Department conducts random quality control testing on all Readymix concrete that is supplied
• How To Decide When To Pump Ready Mix Concrete?
The advantages associated with pumping ready mix concrete are numerous. From a time and money saving perspective, it often cannot be matched. When it comes to placing concrete in difficult situations, pumping is generally the only viable option.
Reasons to use the Lafarge pumping service
Quality
o Easy placement of high quality concrete of uniform consistency
o Pumped concrete is flowable yet highly cohesive
o Pumped concrete is formulated to allow pumping without segregating and with minimal bleeding
Saving time
o The site or the element to be concreted may be difficult to reach. Pumps can bypass this problem quickly
o Pumps place concrete at higher speeds than alternatives
o For high rise projects, placing concrete at various levels is quick and easy
Saving money
o Pumping reduces equipment and plant costs
o Pumping reduces labour costs
Convenience
o Lafarge Readymix pumping removes many of the handling and logistical problems associated with working with large amounts of concrete
o Pumping means concrete is placed directly where needed, easily and efficiently
o Pumped concrete in residential applications
12. Removes the need to build ramps to wheelbarrow concrete onto first floor decks
13. Removes the need to break down garden walls and destroy established gardens to allow for access to Ready Mix trucks or other concrete material delivery vehicles
Ordering concrete to be pumped
Tenders and quotations
If it is decided that the concrete will have to be pumped, there will be a cost of setting up the pump adjustments to mix proportions and the cost of concrete to accommodate pumping
Acceptance and confirmation
Confirm the date and time of your order when the quotation is accepted, or arrange to confirm these details later - at least 72 hours in advance to avoid cancellation fees
Pre-pumping site inspection
o To plan for a pump job, a Lafarge Ready Mix representative will inspect the site to check:
o Access for the pump and truck mixer to maneuver on site
o Equipment needed to complete the job as efficiently as possible
o Whether the operation will be done using a truck-mounted boom pump or a static pump
o Whether there is adequate water supply and washout area on site
o Safety aspects on site
o Special site requirements- some residential areas have curfews on construction work
o That the customer is aware of the pump priming requirements
Important Note:
If Lafarge Ready Mix considers that the site is unsafe, corrective action may be required before the pour is undertaken.
• Additional Factors To Pay Attention To When Pumping?
There must be close communication between the contractor, the Lafarge pumping team and the Lafarge batch plant.
Access: A truck mounted pump and mixers need good access to the site. A truck mixer loaded with 6m3 of concrete weighs 30 tons. The vehicle is 8m long and 2,8m wide. A pump would require a maximum space of 12m in length and 9m width.
Washout Area: A washout area should be provided so that truck chutes can be cleaned and the pump and pipeline segments washed out. Wash water should not be allowed to drain into the sewage or storm water
systems. If there is no place to dispose of washout water, prepare a sandbagged area
Safety: Safety aspects are particularly important when pumping. High pressures are used to force the concrete through the pipeline. All staff not directly involved should keep clear of the area when pumping is taking place. No one should work underneath the boom, in case of boom failure.
Finishing Equipment: More equipment for compacting and finishing will be needed because the concrete is discharged faster. A rough guideline is one vibrator for each 10m3 per hour of concrete placed. A pumping capacity varies according to the pump specifications and application. A guideline is between 20m3 and 60m3 per hour, depending on the project requirements.
Larger or more complicated pours: Large pours may require more than one pump. High rise buildings may entail the installation of a static pump and a pipeline, which will be left in place throughout the building process. In these cases, the prepumping site inspection will be arranged well in advance and the engineer may need to be involved. This needs to be made known to Lafarge at the time of the tender.
Pours over long distances can be handled by Lafarge Readymix. Distances of up to 200m are not uncommon, however it should be remembered that the Lafarge Technical Department will need to adjust the mix design for this purpose.
• How To Place And Compact Concrete?
Concrete placing and compaction has to be right first time. The degree of success will not be fully known until the hardened concrete can be inspected, at which stage it will be difficult and expensive to correct any defects. Important aspects of managing the placement process are the selection of suitable equipment and correctly trained staff.
Productivity: A placement method that transports and places the concrete in a single operation is the most productive approach. The concreting team needs to know what action to take if the appearance of any concrete is abnormal. While being focused on productivity, they must also know that it cannot be achieved at the cost of quality.
Dropping concrete: Developments in concrete technology allow concrete to be dropped much further than before. Whereas traditional construction methods for columns involved numerous construction joints, it is now possible -with the involvement of the contractor, specifier and Lafarge Readymix - to design concrete to pour a 15 meter high column in a single lift. A special concrete has to be designed to meet this special demand.
Also, should such a pour be undertaken it is important to increase the strength of the formwork to cope with the increased hydrostatic pressure of the concrete.
• How To Decide Between Ready Mix Concrete And A Site Mix?
Before starting a project, a decision should be taken between using Ready mix or Site mix. There are numerous benefits from using Lafarge Ready Mix compared with mixing concrete on site. Some of the more important ones are:
Technical: Lafarge Readymix has the resources and technical expertise to provide a range of mixes assuring the user of the right mix design for the application. This is more difficult with small batching operations.
Flexibility: Readymix concrete is better equipped to cope with changes in weather conditions or the construction programme and maintain the projects schedule.
Time: The ease of using ready mixed concrete means that one delivery may be efficiently distributed to various positions on site. Site mixing tends to be time-consuming compared with the speed of discharge of Lafarge Ready Mix Concrete, especially when larger volumes are involved.
Quality control: The quality of the finished concrete should always be of primary concern. Lafarge Ready Mix delivers a guaranteed product which reduces the risk of quality problems. Product from site batching plants, particularly the smaller less sophisticated units, is exposed to a higher risk of failure or lack of consistency.
Access: Some sites have insufficient space to set up a batch plant: ready mixed concrete provides the perfect solution. Where access is also restricted, Lafarge Ready mix offers a pumping service to move the concrete across difficult distances and heights.
Cost effective: Ready mixed concrete is generally the cost effective solution when all cost factors of mixing concrete on site are taken into account. These include the total cost of materials, storage, wastage and theft, hiring and operation of the necessary plant, labour and supervision of an on-site batch plant.
Environmental: Noise: the noise level of a batching plant can become a problem if the site is in a residential area. Lafarge Readymix is able to discharge the concrete at a rate of at least 1m3 every two minutes and is therefore only on-site for a short period of time.
Pollution: batch plants have to be well-managed to prevent contamination or blockage of storm-water drains.
Clean-Up: environmental concerns are reduced when raw materials are not stored on site and a major clean-up operation is avoided at the end of the project.
• Why Choose Lafarge Readymix?
Using Readymix concrete for both large and smaller projects can save time, effort and ultimately money. Some of the benefits of Lafarge Readymix concrete are outlined below.
The possible problems with multiple suppliers:
o Mixing concrete on site means dealing with multiple material suppliers and the associated:
o Stress
o Work stoppages owing to late deliveries
o Work stoppages, overtime and down time
o Additional costs
Lafarge Ready Mix offers you:
o One reputable supplier
o A competitive price
o Scheduling assistance
o On-time deliveries
Mess, storage space and raw materials
o Using Readymix reduces the mess associated with building as well as the space required for stockpiling materials.
The use of Lafarge Ready Mix concrete helps prevent:
o Clean-up costs for the garden and house interior
• How To Sample And Test Concrete?
operation to carry out rigorous quality assurance testing on all its products. The routine tests are conducted in accordance with SANS standards.
The Lafarge laboratories also provide an unequalled service to customers who may need assistance to comply with any other established standards or with problem solving. Successful testing requires good sampling procedures. These are outlined below:
Sampling concrete from a Readymix truck (SANS Method 861-2:2004)
Purpose - To lay down a procedure to achieve consistent representative samples. If the sampling is not done correctly, the test results will be incorrect and invalid.
Equipment - Corrosion resistant metal scope, Shovel and wheelbarrow or other suitable container
Procedure:
o Take the samples from the stream of concrete being discharged from the truck's mixing drum. Do not sample the first and last 10% percent of the load
o Hold the sampling scoop as close to the discharge point as possible. The concrete should not be allowed to freefall more than 500mm
o Take at least nine samples at equally spaced intervals during the discharge
o Mix the nine samples to ensure the overall sample is uniform
• Is The Weather Important?
Extreme temperatures and rain can all cause problems. Protection with plastic sheeting and hessian may be needed to prevent the concrete freezing or the surface washing off. Where needed a mix design can be changed.
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