Civil Engineering nOVEMBER 2021 | Vol 29 No 10

Civil Engineering November 2021 55 I n Br i ef F ollowing the demise of the South African Readymix Association, surface mining industry association ASPASA has found that new entrants often don’t understand the issues and the use of readymix concrete and how to order it. By sharing best practices with readymix cus- tomers, ASPASA members hope to create a more sustainable readymix industry. ENQUIRIES AND TENDERS As much information as possible should be provided to the readymix concrete company at the enquiry or tender stage. The contract specification may contain specific information pertaining to con- stituent material restrictions, minimum cement content, contents and maximum water cement ratios. It is therefore essential that the readymix concrete supplier has sight of this order to determine if the locally held mate- rials will be suitable or whether alternative materials need to be sourced. If you do not supply the full contract specification the incorrect concrete may be ordered. Additionally, it is essential that the correct consistency and workability requirements are specified for the job. An estimate of the volume of concrete required is also essential, while any additional information pertaining to placement rates would be useful for forward planning. PLACING ORDERS To avoid confusion, always refer to the quotation and concrete reference number or letter when ordering rather than refer- ring to the concrete description or part of it. Your order and subsequent delivery of readymix concrete will be based upon the requested consistency and workability. Additional costs may be incurred if the original consistency or workability of the concrete is increased. Always order the correct consistency for the job rather than adding water on site. This is a bad practice and will adversely affect the quality of the final product. It will also void any guarantee with regards to the concrete. NEW READYMIX CUSTOMERS Readymix concrete companies will usually advise on and recommended the concrete to be used (based on relevant SABS 878 standards) and will also be able to help with calculating the quantities and volume of concrete required. Ask about the use of self-compacting concrete as this may be an ideal option for ease of placement and reduced time, effort and overall costs. However, this is only suitable for projects where the top surface is approximately level. Coloured and pat- tern imprinted concretes are also available. CORRECT PLACEMENT On arrival at site, the readymix concrete is discharged in a controlled manner down a chute that extends approximately 7.7 m from the back of the vehicle. The chute can be maneuvered from side to side, and to a limited extent vertically to assist in discharging the concrete as close as pos- sible to its final position. Some readymix concrete companies can offer specially designed delivery vehicles that incorporate either a concrete pump or conveyor – consult with your supplier regarding availability. Safe access for the delivery vehicle must also be provided, taking into consid- eration the size and weight of the loaded truck, the ground conditions, and access. Always consider how the concrete is to be moved from the point of discharge to its final position prior to placing an order. PART LOADS Part load charges may apply and will be built into the quotation at the enquiry stage. If a user under-orders and requires an additional delivery to complete the job, this may be relatively expensive due to the application of further part load charges. Readymix concrete companies will need a period of time for adequate dis- charge, which is free of charge. However, charges may be incurred following expiry of this period. Please be aware that if you have over-ordered and wish to return any readymix concrete that has not been discharged, a charge may be incurred. The production, ordering, delivering and handling of concrete ordered is not a simple exercise and a reputable readymix supplier should always be used. HEALTH AND SAFETY Where skin is in contact with fresh con- crete, skin irritations are likely to occur and can range from dry skin to irritant contact dermatitis, and severe burns in cases of prolonged exposure. Users should take precautions to avoid dry cement entering the eyes, mouth and nose when mixing mortar or concrete by wearing suitable protective clothing. If cement or concrete enters the eye, immediately wash it out thoroughly with clean water and seek medical treatment. Take care to prevent fresh concrete from entering boots and use working methods that do not require personnel to kneel in fresh concrete. Wash wet concrete off the skin immediately. Barrier creams may be used to supplement protective clothing but are not an alternative means of protection. Readymix concrete is heavy, with a standard wheelbarrow load weighing over 100 kg. Lifting even a small volume may cause physical injury and health and safety regulations must be followed. USE OF EQUIPMENT Certain types of plant equipment create a significant vibration during use. Prolonged exposure to vibration can cause hand arm vibration syndrome (HAVS). Reduce the effects of vibration by selecting plant with vibration dampers, using antivibration gloves, taking regular breaks and keeping hands warm in cold weather.  How to work with readymix concrete Readymix concrete being discharged