570.1 Repair of Concrete Surface Failures
570.1.1 Types of Surface Failures
Surface failures of portland cement concrete pavements usually consist of map cracking, scaling and spalling. Map cracked surfaces may be extensive and yet offer no unevenness to traffic. Scaling and spalling in their early stages have no particular effect on the riding quality of the pavement but should not be ignored as both tend to progress and become a serious hazard and objectionable to traffic. Scaling and spalling may be equally deep and rough but result from different causes.
Spalling is a chipping or splintering of sound pavement, usually caused by impact of very heavy loads or by pressure between two slabs. Spalling is usually limited to small areas along the outer edges or along joints or cracks.
570.1.2 Repair of Concrete Surface Failures
1. Map Cracked Areas - Map cracked areas will usually not require maintenance unless the cracks begin to admit appreciable water or the areas begin to deteriorate further. The value of sealing or patching map cracked areas which are not deteriorating is questionable and in some cases will cause more additional maintenance than if left alone. If maintenance is absolutely necessary, a thin seal with a sand-asphalt mix or an asphalt seal applied with a squeegee and blotted with sand is suggested. If map cracking is extensive in nature a resurfacing by contract or thin overlay decks with a high type mix should be considered.
2. Deposit Cracked Areas - Deposit cracked areas where spalling and scaling have occurred may be repaired temporarily by using a sand asphalt or "Black Annie" mix. If the area has not started to spall, but is badly cracked, a light bituminous seal over the cracked areas will prolong the pavement life. In areas where cracking is extensive or has progressed to the final stages, resurfacing by contract should be considered.
3. Scaled and Spalled Areas - Scaled and spalled areas can be classified as shallow, moderate, and excessive. Areas which are very shallow may be better left alone, if rideability is not obnoxious, or if deterioration is not progressing at a rapid rate. However, if desirable, areas with shallow scaling or map cracking may be thoroughly cleaned and sealed with one or more applications of RC cutback or asphaltic emulsion and covered with coarse sand or screenings.
- a. Areas of moderate scaling (up to 1 1/2 in.) should be thoroughly cleaned, lightly primed with cutback asphalt or emulsions and covered with a fine mix asphaltic concrete material or "Black Annie" mix. Cold mix may be used in emergencies, but should be replaced with hot mix or "Black Annie" as soon as practical. Patches should be thoroughly compacted and edges should be feathered to ensure a smooth riding surface. A short period of curing should be allowed before the patch is open to traffic. Curing time will depend on the mix being used.
- b. Areas of excessive scaling (over 1 1/2 in.) may be patched in the same manner as areas of moderate scaling, except the asphaltic concrete or "Black Annie" may require laying in two lifts.
In all bituminous patching, care should be exercised to avoid an excessive quantity of priming material, otherwise rolling or shoving of the patch may result.
570.1.3 Patching Small Areas
Epoxies, concrete accelerator and special fast setting cement mixes may be used to patch small areas of scaling or spalling. However, the use should be confined to important factors in patching scaled or spalled areas, particularly with the higher cost material, is the preparation of the hole or areas to be patched. All loose, deteriorated, and hollow sounding material shall be removed with air chisels or by other means. The hole should be squared up as much as possible and if a concrete saw is available, it should be used for cutting the outside limits of the area to be patched. The edge should be cut vertically and of sufficient depth to eliminate feather edging. The area or hole should then be cleaned out thoroughly by sand blasting or with compressed air, if the sand blast machine is not available. The limitation and usage of these materials are:
1. Epoxies - For patches 1 in. or less in thickness. Epoxy may be used for deeper patches; however, if used, it must be placed in lifts not over 1 in. in thickness, allowing at least 1 hour between lifts. Epoxies take 3 to 4 hours to cure, depending upon the weather. No bonding compound is required; however, the hole is primed with the epoxy material. The epoxy is mixed with the aggregate and spread and finished to the desired cross section. The patch is allowed to dry and cure.
2. Accelerated Concrete - Generally used for patching holes or areas 1 in. or more in depth. This material is fast curing, faster than the epoxy, and requires a wet cure applies immediately after placement. The material has a very short pot life, resulting in the need to place the material immediately. The patched area must be kept wet until ready to be opened to traffic. The amount of accelerator used varies with the temperature, the colder the temperature, the more accelerator used.
3. A special bonding compound can be used with accelerated concrete. If used, only the edges of the hole or area to be patched are primed. Neat cement (cement and water mixture) can be used as a bonding compound. If used, the edges and the bottom of the area to be patched should be covered with the neat cement. The best method to apply is by using a stiff wire brush. It is very important that the neat cement not be allowed to dry before the hole is filled with the patching material.
4. Fast Setting Cement Mixtures - Patching can be done at lower temperatures, with a shorter curing time. The curing time is approximately one hour but with vary depending upon weather conditions and depth of patch. Pavement repairs using such cement is not generally recommended.
Manufacturers recommendations shall be followed in regard to usage and methods with all these materials.