The process of measuring ingredients or materials to prepare concrete mix is known as batching of concrete. Batching can be done by two methods, volume batching and weight batching. Batching should be done properly to get quality concrete mix.
Methods of Batching Concrete
1. Volume Batching
- In volume batching, materials are measured on the basis of volume. It is less precise method of batching
- Measurement boxes or gauge boxes of known volume are used to measure materials.
- Cement is taken in the form of bags, where volume of one bag of cement (50 kg) is taken as 35 liters.
- Volume of Gauge box used is made equal to the volume of one bag of cement which is 35 liters or multiple thereof.
- Gauge boxes are generally deeper and contains narrow top surface and they are made of timber or steel or iron.
- Volumes of different sized fine aggregate and coarse aggregate are measured individually by these gauge boxes.
- Water is measured using water meter or water cans of known volume are used.
- To make 1:1:2 ratio concrete mix according to volume batching, one should take one bag of cement (35 liters) , 1 gauge box of fine aggregate (35 liters) and 2 gauge boxes of fine aggregate (70 liters). If the water-cement ratio is 0.5, then half of the volume of cement which is 25 liters of water should be taken.
2. Weight Batching
- In this method, Materials are measured on the basis of weight. It is accurate method of batching.
- Weigh batchers or other types of weighing equipment are used to measure weight of materials.
- Cement, fine aggregate, coarse aggregate and water are taken by weighing.
- Weigh batchers used are available in two types namely mechanical weigh batcher and electronic weigh batchers.
- In mechanical weigh batchers, weights are measured using spring and dial gauge arrangement and it is widely used equipment in weigh batching.
- In electronic weigh batchers, electronic scales and load cells supported by hoppers are used to measure the weight of ingredients of concrete.
- Weigh batchers available are may be Manual or semi-automatic or fully automatic . Manual type is used for small concrete production job while other two types are used for large concrete production.
- In case of semi-automatic weigh batching, aggregate container gates are lifted manually and it is automatically closed after reaching required quantity in the weighing machine.
- In fully automatic weigh batcher, all the process will be done automatically. The benefit of this type equipment is, it also measures the moisture content present in the aggregate and corrects the required quantity of water-cement with respect to moisture content of aggregates.
- To prepare 1:1:2 concrete mix using weigh batching, measured quantity of materials are 50 kg of cement, 50 kg of fine aggregate and 100 kg of coarse aggregate.
Weight Batching vs. Volume Batching
- Weigh batching is most precise method of batching than volume batching since it is difficult to find the exact volume of granular materials because of their voids.
- Moisture content presence in the aggregate should also be considered while batching. In case of fully automatic weigh batching it can be considered but volume batching is not suitable in such cases.
- Compressive strength of same concrete mix at 7 days and 28 days is higher for weigh batching concrete mix than volume batching concrete mix.
- Weigh batching concrete mix gives medium to very high slump while for the same mix proportion in volume batching, slump differs from low to high.
- Volume batching does not require skilled workers but weigh batching.
- Selection of batching method depends upon size of project, concrete production rate.