Popouts are caused by unsound coarse aggregate particles near the surface of the concrete. These particles readily absorb water, and under freezing conditions, they expand and destruct, popping off the thin surface layer of mortar above. The resultant hole is a perfect spot to hold water which can freeze in cold weather and cause further destruction. Further popout problems are best avoided by treating the entire surface area with a water-repellent liquid sealer to prevent further water absorption. The holes may be filled with acrylic compounds or latex modified mortars that are self-bonding.
Dusting is indicated by the presence of a fine whitish powder on the surface of floors. Usually, dusting is caused when the surface is troweled while bleed water is still on the concrete surface. One or two applications of a solution of magnesium fluosilicate and zinc fluorosilicate will usually cure the problem. This solution is sold in most hardware stores and lumber yards under various trade names, in both liquid and powder forms.
Saturate the dusted surface by sloshing the solution on and spreading it over the entire area with a mop or broom. Bubbling will be noticed during the application and is to be expected. A definite improvement will be noted within 24 hours. Where necessary, make a second application in the same manner.
Honeycombing, can be caused by using a cement mix with excessive coarse aggregate, by leakage of mortar through the forms, by very low slump concrete, and by improper or insufficient vibration. Besides creating an unattractive appearance, the honeycombed area can be a weak link in the structure.
When preparing small honeycombed areas, as when repairing small holes, people are likely to scant on surface preparation. The result of this frequently causes the patch to dislodge. Removal of all loose aggregate particles is essential for satisfactory repair. All exposed aggregates and crevices must be wetted and a good bonding agent applied. The more commonly used materials are epoxies, expanding mortars, and Portland cement mortars. The material chosen should be dense and must be pressed firmly into place. When the area to be repaired is large, it might be better to use a form. Some are formed completely, and the repair material is injected under pressure through ports in the form. Another method is to leave an open space at the top of the form, and then to place concrete, similar to the original mix, through the opening and compact it well. After the concrete has hardened enough to permit form removal, the area previously left unrepaired is then patched.
Cavitation, very similar in appearance to honeycombing, can appear months or years after the concrete has been placed. Wherever there is a flow of water passing a protruding object, or an uneven vertical wall, cavitation may appear on the downstream section of the irregularity. It has been suggested that the bubbles created by the protrusion burst, and so create the phenomenon. Use the same repair techniques for cavitation as for honeycombing, being sure to produce an even surface.
Cold joints in mass concrete, are caused by improper placement of the plastic concrete. Delays in placement, failure to place the concrete in horizontal lifts, and inadequate vibration are among the many reasons for cold joints. True, the strength of concrete is dependent on the compressive strength of the concrete mix and the amount and placement of the reinforcing steel. Yet in mass concrete,the steel does the major job with the concrete being, more or less, a filler. An overly rich mix can only add to the heat of hydration and help create a cold joint situation. Regardless of the ambient temperature, the addition of a set-retarding admixture will reduce the potential for cold joints.
When a cold joint occurs during placement because of delivery delays, and the concrete cannot be revibrated to a plastic state, a thin layer of grout, before continuation of placement, will pay dividends. The epoxy injection system is the best method of repair.
Call Concrete Salt Lake City for professional concrete work in the and around the Salt Lake City area.