There are two methods used for mixing the ingredients: hand and machine. Twin shaft concrete mixer is one kind of compulsory type concrete mixer. The mixer will be helpful for your construction jobs. It is important no matter which method is employed, all materials- water, cement, sand, and gravel- must be measured. Only a limited amount of water should be used when making a concrete mix. If too much water is added the cement paste which holds the mass of sand and gravel together will be diluted and weak. Weak cement paste will produce weak, porous concrete.
Materials may be measured as follows: Use a pail marked off in gallons and half gallons for measuring water. Use a 1-cubic-foot bottomless measuring box for measuring sand and gravel. This box is of simple construction and can be made in the home workshop. Portland cement is usually obtainable in sacks, each sack holding 1 cubic foot. Cement in quantities of less than one sack may be measured as portions of cubic foot in the bottomless box. On small construction site, small concrete mixers for sale and hand operated cement mixer are your choice.
Until a recent discovery that the strength, durability, and watertightness of concrete depend upon the proportion of water to portland cement, mixtures were specified as one part of cement to a certain number of parts of sand(fine aggregate) and gravel or pebbles( coarse aggregate). It has been found that it is more practical to give the amount of mixing water required for each sack of portland cement, varying the amount according to the type of work. For example the recommended mixture for sidewalks is 5 gallons of water per sack or cubic foot of portland cement when both fine and coarse aggregate are wet. The moisture in the wet aggregates will act on the cement, and less water is added in this particular case than if the aggregates were absolutely dry. Had the aggregates been dry, the correct amount of water for every sack of portland cement would be 6 instead of 5 gallons. It is therefore evident that to get the best results, all of the ingredients used must be in the proper proportions.