Concrete Foundation Repair

Selecting the most satisfactory protective treatment depends greatly upon correctly assessing the exposure environment. Concrete sealing compounds and coatings that provide good protection from weathering in an essentially dry environment may perform poorly in abundant water, such as on some bridge curbs and railings, stilling basin walls, and piers. Freezing and thawing tests of concrete specimens protected by various concrete sealing compounds and coatings, including linseed oil, epoxy and latex paints, chlorinated rubber, and water-proofing and penetrating sealers, have been performed in Reclamation laboratories. These tests indicate that proprietary epoxy formulations, silicone and saline formulations, and high molecular weight formulations excel in resisting deterioration caused by repeated freezing and thawing in the presence of water.

None of these formulations, however, will totally “waterproof“ concrete. That is, they will not prevent treated concrete from absorbing water and becoming saturated under complete and long-term submergence conditions. Except for hand-placed mortar restorations and repair of deteriorated concrete, concrete sealing compounds are ordinarily not applied on new concrete construction. The treatments are most commonly used on older surfaces when the earliest visible evidence of weathering appears. The treatment is best used before deterioration advances to a stage where it cannot be arrested.

Such early evidence primarily consists of fine surface cracking close and parallel to edges and corners. Pattern cracking, surface scaling or spalling, and shrinkage cracking may also indicate the need for protection. By treating these vulnerable surfaces in the early stages of deterioration, later repairs may be avoided or at least postponed for a long time.

Repair home foundations and concrete floors using these tips and techniques.

Excess Concrete Mix Water.—The use of excessive water in concrete mixtures is the single most common cause of damage to concrete. Excessive water reduces strength, increases curing and drying shrinkage, increases porosity, increases creep, and reduces the abrasion resistance of concrete. Figure 16 shows the cumulative effects of the water-cement ratio on the durability of concrete. In this figure, high durability is associated with a low water-cement ratio and the use of entrained air. Damage caused by excessive mix water can be difficult to correctly diagnose because it is usually masked by damage from other causes. Freezing and thawing cracking, abrasion erosion deterioration, or drying shrinkage cracking, for example, is often blamed for damage to concrete when, in reality, excessive mix water caused the low durability that allowed these other causes to attack the concrete.

During petrographic examination, extreme cases of excessive mixed water in hardened concrete can sometimes be detected by bleed water channels or water pockets under large aggregate. More commonly, examination of the batch sheets, mix records, and field inspection reports will confirm the use of excessive mix water in damaged concrete. It should be recognized, however, that water added to transit truck mixes at the construction site or applied to concrete surfaces during finishing operations often goes undocumented. The repair of concrete damaged by excessive mix water is removal and replacement.

However, depending on the extent and nature of the damage, several maintenance or repair methods can be useful in extending the service life of such concrete. If the damage is detected early and is shallow (less than 1.5 inches deep), application of concrete sealing compounds, such as the high solids content (greater than 15 percent) oligomeric alkylalkoxy siloxane or silane systems or the high molecular weight methacrylic monomer system, will reduce water penetration and improve resistance to freeze and thaw spalling and deterioration. Such systems require re-application at 5- to 10-year intervals. Epoxy- bonded replacement concrete can be used to repair damage that extends between 1.5 and 6 inches into the concrete, and replacement concrete can be used to repair damage 6 inches deep or deeper.

Insufficient concrete cover over reinforcing steel is a common cause of damage to highway bridge structures. This can also be a problem in hydroelectric and irrigation structures. Reclamation usually requires a minimum of 3 inches of concrete cover over reinforcing steel, but this can be insufficient in corrosive environments. Concrete exposed to the corrosive effects of sulfates or chlorides should have a minimum of 4 inches of cover to protect the reinforcing steel. Insufficient cover allows corrosion of the reinforcing steel to begin. The iron oxide byproducts of this corrosion require more space in the concrete than the reinforcing steel, resulting in cracking and delamination in the concrete.

Failure to provide adequate contraction joints or make expansion joints wide enough to accommodate temperature expansion in concrete slabs will result in damage. Concrete with inadequate contraction joints will crack and make a joint wherever a joint was needed but not provided. Unfortunately, such cracks will not be as visually attractive as a formed or sawed joint.

Formation of the cracks relieves the tensile stresses and, though unsightly, seldom requires repair. Concrete slabs constructed with insufficient or too narrow expansion joints can cause serious damage to bridge surfaces, dam roadways, and the floors of long, steeply sloping, south-facing spillways. Such concrete experiences large daily and seasonal temperature changes resulting from solar radiation. The resulting concrete expansion is greater in the top surfaces of the slabs, where the concrete temperatures are higher, and less in the cooler bottom edges. Such expansion can cause the upper portions of concrete in adjacent slabs to butt against one another at the joints between the slabs. The only possible direction of relief movement in such slabs is upward, which causes delaminations to form in the concrete, starting at the joints and extending an inch or two back into the slab. These delaminations are commonly located at the top mat of reinforcing steel. In temperate climates, the formation of delaminations relieves the expansion strains, and further damage will usually cease. However, water can enter the delaminations in cold climates, undergoing a daily cycle of freezing and thawing. This causes the delaminations to grow and extend 3 to 5 feet away from the joint.

Repairing damage caused by faulty design is futile until the design faults have been mitigated. Embedded metal features can be removed, handrails can be provided with slip joints, and guardrail attachment bases can be moved to locations with sufficient concrete to withstand the tensile forces. Mitigating insufficient concrete cover over reinforcing steel is very difficult, but repair materials resistant to those types of corrosion can be selected for the repair. Concrete sealing compounds or coatings can also protect repairs to reduce water penetration. Slabs containing inadequate expansion joints can be saw cut to increase the number of joints and/or to widen the joints to provide sufficient room for the expected thermal expansion.