Home Sustainable Land Development Today February 2005

A Natural Solution to a Natural Problem

Written by Administrator

Wednesday, 02 February 2005

Poor soil conditions can be mitigated. If there is one thing that contractors and developers wish they could control, it is the weather. Perhaps nothing is more disruptive and frustrating to a project’s schedule than delays imposed as a result of extremes in the area of rain, snow, wind, heat, and cold. These challenges, as well as those caused by utilizing site-soil as structural fill to raise grade elevation of building pads and paved areas, are also common when trying to attain the a stable soil meeting the soil moisture content and compaction requirements that is needed or required. One of the proven solutions to these problems is through the application and use of lime. Lime can be used for drying, modifying, or stabilizing construction site soils. In fact, one major supplier, Carmeuse Lime, Inc. explains that lime’s use produces seven advantages for construction site soil:     1. Promotes moisture control and drying     2. Increases soil workability and compaction     3. Reduces soil plasticity     4. Reduces soil swelling     5. Creates a solid working platform for heavy equipment     6. Improves quality of engineered fills and embankments     7. Extends the construction season Also, as a natural chemical compound, when used properly in construction applications, is environmentally friendly. Successful Implementation Ralph Bardine, Vice President of Sales-- Construction Industries with Carmeuse, recalls a situation in the southeastern U.S. where building structures were already constructed on a site with high clay content. The problem was, that with a roof already overhead, environmental influences like the sun and wind had been eliminated as options for reducing the moisture content in the soil base. Subsequently, the pouring of the concrete pad would have been critically delayed. “This, obviously, isn’t the ideal situation for any developer,” explains Bardine. “However, we were able to work with the contractor to provide the lime and the expertise on how to mix it with the soil. The addition of lime resulted in optimum moisture content and allowed the contractor to achieve proper soil compaction. In another example, the Indiana Department of Transportation (INDOT) defied common construction limitations when it started a large excavation and embankment project in the dead of winter. INDOT, after consultation with geotechnical engineers with Professional Service Industries Inc. (PSI) of Indianapolis and soil stabilization specialist in the area it was determined that lime kiln dust (LKD) would be the best lime product for this project. “LKD causes a number of things to happen that affect soil moisture and compaction,” explains Larry Cole, a technical manager in the construction division of Carmeuse. “Water is absorbed as CaO becomes Ca(OH)2. This process, called hydration, lets off heat and drives off water through increased evaporation. The heat of hydration had an additional benefit of warming the soil on this project allowing more time for the contractor to compact the treated soil and cover the layer with more soil before it could freeze.” Construction began on December 26, 2002, and continued 24 hours per day, seven days per week, with only a few stops when snow or rain forced a temporary shutdown. By early April, the freshly placed layers of soil would not freeze during the night. By May, over 1 million cubic yard of embankment had been built to support key highway structures. For another case, this time using quicklime, an eastern Pennsylvania project, had two building pads (725,000 sq ft and 675,000 sq ft) for floors that needed to be poured on raised elevations from 5-8 feet of structural fill. However, heavy snow in March and a cool spring featuring frequent rain, resulted in a soil moisture content varying from 20-30 percent. Optimum moisture was determined by the project geotechnical engineer, MACTEC, Inc., to be about 17 percent to achieve maximum density using standard proctor compaction effort (ASTM D698). Additionally, the natural soil was 35 percent clay, making it even slower to dry, and soft and sticky when wet. Handwerk Contractors (Harrisburg, PA), an affiliate of Haines & Kibblehouse, Inc., worked with Recon Construction Services, Inc. (York, PA) to add and spread the quicklime onto the soil. Using two spreader vehicles, typically applying 3.5-4 percent lime by dry weight of soil, they mixed the soil and lime to a depth of 12 inches with two rotary mixers. Lime can have three beneficial effects on fine grain soils-drying, modification, and stabilization. In this case, drying was the primary goal, but the lime also modified the soil, making it less plastic and more friable, thus aiding compaction. The effective change in moisture content dried the soil enough to meet the job specifications for the large majority of the soil. The result-a solid pad for the buildings’ floor. Preplanning Saves Time and Money Like virtually everything in the land development industry, the element of timing is very important. The same holds true for determining the use of lime on a project. According to Bardine, “Planning and preparation are important because typically the engineers, developers, and/or contractors are constrained by a tight timeline. Ideally, the lime supplier and geotechnical engineer work together to specify the appropriate stabilization solution. Unfortunately, this is not always the case. On occasion contractors can encounter changes in soil conditions causing them to run into severe problems. This requires lime be included after the fact in order to maintain their schedules. Carmeuse, with its headquarters in Pittsburgh (PA), produces and distributes lime products throughout the eastern and central United States and Canada. It also provides a number of services relating to the use of its products. They have a number of technical personnel, including a staff of engineers and chemists, that will assist in determining what products are best suited for each situation. Most importantly, they will help with the logistical challenges of getting the product to where it is needed when it is needed. “Whether it is a small developer needing just a couple tons of lime or a large project that requires tens of thousands of tons by rail,” we will work with a customer to determine the best solution” stated Bardine. Other top producers of lime in the United States are Chemical Lime Company, Mississippi Lime, and Graymont Lime Company. Educating the Masses “The key to maximizing the benefits of lime stabilization is to use a qualified stabilization contractor,” was a final point stressed by Bardine. One of the tools used by Carmeuse to educate developers, engineers, and project managers on soil management, and the possible benefits of lime, is to provide free half-day workshops. The workshops are jointly presented by Carmeuse and a qualified regional contractor. The workshops present comprehensive technical information that assist the attendees to:     1) Select the appropriate reagent for various soil types.     2) Take full advantage of the structural improvements of lime stabilized soil.     3) Incorporate the best practices and construction techniques to minimize costs and maximize time savings. “Some of the best land development contractors we’ve worked with,” claims Bardine, “have attended every workshop that Carmeuse has held.” SLDT