Bowing Block Basement Wall Repair

Unknown to many homeowners, there is an enormous amount of force being supported by a typical basement wall. For a sandy, water soaked soil there can be as much as 2600 pounds per linear foot on an 8 foot high wall. Unfortunately the typical masonry and concrete basement walls built in 20th century were not designed to take these stresses long-term which results in horizontal cracking, bowing, and may end with failure of the wall. Fortunately for homeowners, StrongHold has cost effective Carbon Fiber solutions which provide remarkable structural benefits without the drawbacks of typical steel beam or steel tie-back installations.

In most residential situations where bowing basement walls occur there are several sets of forces which interact to cause the problem. The largest mobilizing force is the addition of lateral earth pressure (soil forces) in conjunction with hydrostatic pressure (water forces). These forces put a horizontal load on the wall which in turn creates a large amount of bending stresses on the masonry or concrete. The bending stress creates an unbalanced condition within the wall due to the very low tensile capacity of concrete and masonry, causing horizontal cracking in the structure. The weight of the structure above the wall helps generate a stabilizing compressive force on the wall until the lateral deflections become too large. As the wall deflects beyond the “center of mass” of the above structure a phenomenon known as the “beam-column effect” creates additional bending stresses on the damaged wall, speeding up deterioration (seen in the image on the right). StrongHold Carbon Fiber Reinforced Polymers (CFRP’s) provide the required additional tensile force needed to fully develop the compressive strength and create a “balanced” situation within the wall to prevent further bowing and cracking.

Testing Results

As a University of Arizona technology-transfer company, StrongHold’s carbon systems are supported by over 20 years of extensive testing and research. These proven systems were tested under numerous federal grants sponsored by the National Science Foundation. Testing was conducted to determine the effect of FRP’s on the flexural capacity of masonry walls as well as the bond strength of the FRP’s to different materials in adverse conditions (acidic environments (pH 2.5), moist environments, alkaline environments (pH 12.5), salt water, etc).

Flexural Testing

The results of the flexural testing for increased flexure capacity were remarkable. According to the NSF technical papers produced by the University of Arizona and published in the Journal of Composites for Construction and American Concrete Institute’s Structural Journal the StrongHold carbon fiber increased the flexural capacity of Un-Reinforced Masonry (URM) walls by up to 450% over the original capacity. Walls already equipped with steel reinforcement also showed a similar increase. Furthermore, the modes of failure in these tests were ductile (occurred slowly, predictably) and not brittlely; thus preventing sudden, catastrophic failures.

Shear Testing

In addition to providing an increase in flexure capacity of basement walls, the StrongHold products are supported by shear capacity tests as well. In shear capacity tests conducted on clay bricks over 500psi was generated prior to the debonding of the carbon system. That means a 12″ wide strip of StrongHold Carbon Fabric on an 8′ wall has nearly 600,000 pounds of potential tensile capacity to strengthen the existing wall. (For conservative design however, StrongHold limits the shear capacity to 200psi).

Durability Testing of Bond Adhesion of StrongHold to your Basement Wall

It is important to assure long term durability of the composite FRP bonded to basement walls. A published research paper titled “Accelerated Testing for Evaluating the Reliability of FRP Bonded to Concrete and Steel Under Severe Environments” provided information regarding the ability of composites to maintain their bond strength when subjected to: – Seawater – Hydrochloric Acid (pH 3) – Freshwater – Caclium Hydroxide (pH 12) – Temperatures to 140° – Relative Humidity of 95% at 100°F – Accelerated UV There were approxiamately 2400 tested specimens for each substrate (steel and concrete) and the results showed StrongHold products have excellent durability when bonded to both steel and concrete even in severe environments. Severe pH environments typically showed a 10-20% early reduction in strength, simlilar to the hot-humid specimens. Even in these incredibly unforgiving, accelerated environments the bond strength showed no significant degredation in relation to structural capacity. This shows that in typical residential conditions (without pools of sulfuric acid or constant 140°F temperatures), the bond strength will remain unchanged even after long periods of time.

Conclusions

StrongHold products provide our customers with a durable, high strength, and aesthetically appealing fix to the common problem of bowing basement walls. The repairs are waterproof and can enhance the flexural capacity of steel reinforced and un-reinforced masonry walls by over 4 times the original capacity. The high stiffness of these Carbon-based products can stop lateral wall movement virtually instantaneously without the problems associated with steel alternatives including corrosion, aesthetics, obstructions, and lower strength capacities. The StrongHold polymers used to bond the Carbon systems to your basement wall have been successfully tested over 20,000 hours of continual exposure to resist chemicals, temperatures, and moisture much more aggressive than typical basement environments assuring a long-term repair.