Concrete As The Building Blocks of Civilization
From as far back as 6500 BC, man has found ways of using self-cementing materials to build slabs for homes, cisterns for water, and kilns to provide mortar for walls. Much like these ancient people, modern man has found a plethora of other uses for concrete. From the Numidians to the Egyptians, from the Numidians to the Romans, from the Romans to the Medieval age, and on and on throughout the history of civilization, self-cementing materials have quite literally been the building blocks of life. It was not until the Industrial Revolution when the English began to mass produce and export cheap “Portland” cement that the world changed to its current state, with massive construction projects being the norm. Now we live in an age of concrete, so much so that if one were to walk down a road in any city, town, or man-made environment, the influences of concrete all around will assuredly be seen.
Why Does Concrete Settle and Sink?
Alongside these great advances in concrete have come the great burden of keeping all that weight at its original level. To understand why this problem exists, you must first understand two basic factors involving any type of concrete structure; weight and soil. The weight of the concrete directly impacts the ability of the soil to hold the structures weight. A single cubic yard of concrete weighs approximately 4,050 pounds. To put that into perspective, the Pentagon in Washington DC was made with 1,660,500,000 pounds of concrete (410,000 cubic yards of concrete throughout the facility). That means that the soil beneath The Pentagon is taking the pressure of all that concrete, not to mention human and other “live weight”. In some areas of the world the soil is naturally densified for bearing such weight or is reinforced with natural materials such as limestone. In many other areas, however, such as Florida and Virginia, the soil is loose and subject to shifting or settling making it much more difficult to build solid foundations for concrete structures.
The Beginning of Mudjacking
The most common and frustrating nuisance with pouring concrete is that after time the concrete’s weight begins to affect the soil beneath it. Even if poured perfectly with a foundation, the soil may push away due to the extreme pressure. As this happens the concrete begins to sink, eventually leading to cracking and crumbling. In wetter climates the soil can be affected by erosion and soil washout from rain and other underwater streams. Whatever the reason for the concrete settlement, historically there was no repair options available. Concrete would simply be set, age, crumble, and eventually be torn out and replaced or left in ruins. This all changed when a man in the small town of Burlington, Iowa by the name of John W. Poulter, an Iowa State Highway Commission Mechanic, finally came up with a solution that could not only save the concrete but leave a lasting foundation to prevent further settling from occurring. He created a device that utilized hydraulic pressure to pump a mixture of dirt, water, and Portland cement through holes that had been drilled into the cement. At the time it was believed that once this mixture settled and hardened it reinforced the concrete, raising it to its original level, and preventing any further damage to the concrete. A national report was released on this miracle process dubbed “Mudjacking” which led to the mass production of Poulter’s device, and thus an industry was born.
For nearly a century mudjacking served its role as the go-to concrete lifting solution as it was much more cost effective than tearing out and replacing the old concrete. However, over time the downfalls to the mudjacking process started becoming apparent. The weight of the injected material can cause further long term settlement if the subsoil is poor. There have also been price increases as building standards and legislation have been passed.
Foam Injection Takes The Market
High density polyurethane foam has found a use in many aspects of construction including insulation and roofing, and is now being used as an injected system to support and stabilize concrete slabs. Polyurethane foam lifting is a process in which a two part polyurethane foam system is injected beneath a concrete slab. Once underneath the slab the chemicals react and expand to 30 times their original size, finding and consolidating any weak soils. In this way the soil is densified and reinforced, without adding any additional unwanted weight to the substrate that could lead to further problems down the road. One primary property of expanding foams is that their expansion will follow the path of least resistance, expanding in all directions to fill any weak soil that needs reinforcing. Closed cell polymer foams offer benefits that go beyond the goal of leveling hard surfaces. They will not retain moisture, which in northern climates can cause frost heaving, and they are not subject to erosion once in place. These distinctive characteristics make the foam injection process the most recent step forward in man's quest for a solution to damaged infrastructure.