Some vital points to be remembered before purchasing ready mix concrete
The ready mix concrete is better as compared to the ordinary concrete mix since it needs less labour, time, efforts and cost. It facilitates to retain homogeneous quality during the work and provides the high speed of concrete construction.
With ready mix concrete, various types of issues like inferior workability, segregation, and bleeding, inappropriate water cement ratio, insufficient mixing time can be easily resolved in the construction site.
Prior to order ready mix concrete, the following points should be taken into consideration :-
01. Grade of Concrete or Mix Design
? Types of work where the concrete will be poured i.e. foundation slab, floor slab, pavements, etc.
? Grade of concrete necessary on site, i.e. M15, M20, M25, M30, etc.
? Slump of concrete both at the batching plant and at the job site.
? The quantity of concrete in cubic meter or cubic yard.
? Address or place of concrete pouring.
? Time of requirement of ready mix concrete on site.
? Time of interval among the two consecutive deliveries of RMC (in the case of higher quantity i.e. exceeding 6 cubic meter).
02. Fly Ash should not be used extra: It is essential to get the proper ratio of fly ash in the concrete. Some RMC producer includes extreme amount of fly ash in concrete which aren?t suggested also by the standards.
Generally, the fly ash is added in concrete at levels which vary from 15% to 25% by mass of the cementitious material component. Plant owner accomplishes this so that the cost is decreased and the profit is raised. So, the purchase should be careful for buying RMC at lower rates, and not get deceived with this lower rates.
It is also essential to get the source of every concrete ingredients (cement, aggregates, admixture, and water), the ratio and quantity of the concrete material per cubic meter, and the types of admixtures applied in RMC. So, prior to give order for ready mix concrete, obtain the above information. i.e. details of mix design from dealer.
03. Source of materials: The RMC dealers buy various concrete materials from diverse sources. The quality of materials may not be always good. So, all the sources should be assessed carefully. If their sources are recognized in the local market for the quality, then the ready-mix dealer can be selected, who will purchase the concrete materials from those renowned sources.
04. Time for Transportation: According to IS 4926:2003, it is recommended to pour the ready mix concrete within 2 hours from the time of loading at the central batching plant. However, a higher period is allowed if retarding admixture is utilized. But, determine the type of retarder used and all steps are followed as suggested by retarding manufacture.
05. Application of Admixture: Sometimes the extra dose of admixture is included at the project site to retrieve the workability of concrete. Some admixtures have chlorides, and if so, it is required to get the amount of chloride content in percentage of the total mass of admixture. If the amount of chloride is increased in ready mix concrete, it will lead to corrosion of the reinforcement steel and the service life of the house or building will be significantly affected. Hence, such admixtures should not be used.
06. Test of Concrete: It is indicated in standards that the ready mix concrete dealers should arrange test facilities at its premises to conduct routine tests, i.e. concrete slump test, concrete cube testing, etc. So, it is possible to double check the workability and strength of ordered concrete.
The workability of concrete can also be verified with slump test on site. Slump of concrete is primarily based on the condition of placement and the requirement of degree of workability. According to IS 456:2000, low reinforced sections like slabs, beams, walls, columns, etc. are casted with the slump of 25 to 75 mm. Heavily reinforced sections like slabs, beams, walls, columns, etc. are casted with the slump of 50 to 100 mm. From slip form work or pumped concrete, the appropriate slump of concrete is 75 to 100mm.
07. Information about Delivery Ticket of Ready Mix Concrete
The information given below, should be providedd in the ready mix concrete delivery ticket for each batch:
? Name and number of the ready-mixed concrete plant.
? Date and serial number of the ticket
? Truck Number
? Name of the purchaser and location of the site
? Grade of concrete
? Mix design details
? Type and size of concrete ingredients and their weight in table format.
? The quantity of concrete in the cubic meter
? Time of loading
? Slump results at the batching plant
? Signature of the concrete plant operator
The information given below, is required to be filled on ready mix concrete ticket on site.
? Time of arrival on site
? The time when discharge was completed
? Any water/admixture added on site
? Location of pouring of concrete
? Slump test result at the site
? Signature of RMC receiver