A fairly recent nationwide survey indicated that 61 percent of industrial concrete floors have caused trouble. Another survey ranked floors as the third most troublesome item in new construction. Certainly this is an area where there is great room for improvement. Fortunately good concrete floors can be constructed with a minimum increase in cost and effort. For a slab on ground the first requirement is a site with good drainage or one for which drainage is otherwise provided. Proper site and subgrade preparation can help greatly in reducing settlement cracking and wet floors, which can occur in even high quality concrete if these things are not properly attended to. Materials used in the concrete should be of good quality meeting ASTM or other applicable specifications. Assuming the use of sound, hard aggregates, concrete floors to be covered with some other material such as tile or carpeting, can be built satisfactorily with a 3,000 to 3,500 psi mix. By this, however, is meant a floor with concrete surfaces of 3,000 to 3,500 psi. Often the concrete bleeds to such an extent that fines and laitance are brought to the top to the slab and the water/cement ration at the surface is greatly increased. The result is a weak floor. Bleeding can be minimized in several ways. One approach is to use the least possible mixing water and place the concrete at a low a slump as possible. The amount of mixing water can be further reduced by water reducing admixtures. Bleeding can be further reduced by air entrainment.
