Lime Kiln Dust and. Self-Cementing Fly Ash. for Drying and Improving Soil at the Construction Site

Transcription

1 Lime Kiln Dust and Self-Cementing Fly Ash for Drying and Improving Soil at the Construction Site Technical Report Effects of Lime Kiln Dust and Self-Cementing Fly Ash to Dry and Modify Soil Lawrence W. Cole, P.E. Technical Marketing Manager--Construction Steve Tutokey Senior Technical Service Technician Carmeuse Lime Company 36 Neville Road Pittsburgh, Pennsylvania 122 This publication provides a summary of findings from Carmeuse Lime & Stone Company Technical Report #4 - Effects of Lime Dust and Self-Cementing Fly Ash to Dry and Modify Soil (TR-4). TR-4 is available upon request from Carmeuse Lime & Stone Company, Pittsburgh, Pennsylvania.

2 Why is lime and lime kiln dust so effective for improving soil at the job site? A common challenge faced by site developers, earthwork contractors and paving contractors is overly wet soil conditions. At many job sites, the existing soil is too wet to be properly compacted as fill for embankments, building slabs, backfill and other uses. Such soil will not support construction vehicles and makes a poor foundation for roadways, parking lots and other paved areas. Additionally, many fine grained soils contain clay particles that increase the soil plasticity. Wet plastic soils are "gummy and sticky," difficult to compact, have low bearing strength and are slow to dry. This causes problems for construction and delivery vehicles, messy job sites, and inefficient grading operations. More importantly - wet, soft, plastic soil at the job site leads to construction delays that cost the contractor and owner time and money due to inefficient construction activities and lost business revenue. Lime products (quicklime, hydrated lime and lime kiln dust) are very effective agents for rapid soil drying and plasticity reduction, with a proven history of use throughout the world. Lime products are particularly effective because they decrease the soil moisture content while increasing the optimum moisture content for compaction - a combined effect referred to as "net effective drying." Additionally, lime products modify the texture of soil containing clay - decreasing the soil plasticity, making the soil less sticky and more friable - crumbly to the touch. Does self-cementing fly ash work as well as lime products for improving soil at the job site? Other chemical agents, including self-cementing fly ash, also have benefits for improving the soil at the construction site. Properties of self-cementing fly ash are described in ASTM D 239 (Reference 1). Pound for pound, which material is more effective for improving the soil at the job site? A laboratory study (Reference 2) to determine the relative effectiveness of lime kiln dust and self-cementing fly ash to dry and modify soil helps answer the question. This laboratory study evaluated the effects of one lime kiln dust (LKD) and one self-cementing fly ash (SC fly ash) for soil drying and reducing soil plasticity on three separate soil samples from northern Illinois. The reduction in soil plasticity was determined by measuring the reduction in Plasticity Index (PI). Additionally the effects of LKD or SC fly ash to rapidly increase soil strength - measured by the increase in CBR - were also determined. References: (1) ASTM D Standard Practice for Characterizing Fly Ash for Use in Soil Stabilization, ASTM International, 1 Bar Harbor Drive, West Conshohocken, Pennsylvania. (2) Cole, L.W. and Tutokey, S., "Effects of Lime Kiln Dust and Self-Cementing Fly Ash to Dry and Modify Soil", Technical Report #4, Carmeuse Lime and Stone Company, 36 Neville Road, Pittsburgh, Pennsylvania, 27. Lime...the proven solution.

3 LKD or SC fly ashwhich is more effective for soil drying? Figure 1 shows that, 4 hours after mixing, LKD is significantly more effective than SC fly ash for drying these soils. For most soil drying applications, LKD is typically spread and mixed at a rate of 3% - % by dry weight of soil. At this application rate, LKD provides twice as much net effective drying for two of the soils, and 6% more net effective drying than SC fly ash for the third soil. At typical LKD use rates, LKD provides, on average, 9% more net effective drying than SC fly ash for these soils. Soil Moisture Decrease + OMC Increase % LKD % LKD 3% Fly Ash % Fly Ash 11% Fly Ash 14% Fly Ash DuPage County Soil Cook County Soil Lake County Soil Figure 1 How much SC fly ash is needed to achieve the same effective drying as LKD? In Figure 2, the red arrows show the amount of LKD or SC fly ash needed to achieve a similar level of net effective drying. For these soils, it requires 11% to 14% SC fly ash by weight of dry soil to provide the same amount of net effective soil drying as 3% LKD. Soil Moisture Decrease + OMC Increase % LKD % LKD 3% Fly Ash % Fly Ash 11% Fly Ash 14% Fly Ash DuPage County Soil Cook County Soil Lake County Soil Figure 2 Contact us at:

4 LKD or SC Fly Ash - which is more effective for soil plasticity reduction? The effectiveness of LKD and SC fly ash to reduce soil plasticity can be evaluated by comparing the reduction in Plasticity Index (PI). Figure 3 shows the PI of each soil at 4 hours and 24 hours after the addition of % LKD or % SC fly ash. The LKD was much more effective in lowering the soil PI than was the SC fly ash. This is due to the significantly higher amount of "available lime" in the LKD - the key ingredient that causes soil modification. In all three soils evaluated in this study, the decrease in PI from the SC fly ash was negligible. Note that most of the PI reduction from the LKD occurred within the first 4 hours. Coupled with the rapid effective soil drying afforded by LKD, it is evident that for these mid-range plasticity soils, field compaction can begin shortly after the LKD mixing operations are complete. Soil Plasticity Index (PI) Untreated Soil % LKD at 4 hrs % LKD at 24 hrs % Fly Ash at 4 hrs % Fly Ash at 24 hrs DuPage County Soil Cook County Soil Lake County Soil Figure 3 How does the treated soil look and feel? There is also a notable difference in the look and feel of soil treated with LKD or SC fly ash. In the study, the LKDtreated soil felt crumbly and friable, while the SC fly ashtreated soil remained sticky and cohesive. This was also visually evident as shown in Figure 4, taken 4 hours after mixing. Untreated Soil LKD-Treated Soil Figure 4 SC Fly Ash-Treated Soil Visit us at:

5 What are the rapid changes in soil strength due to LKD and SC fly ash? During construction operations, stronger soil is better able to support construction vehicles and equipment, creating a sound working platform. Strong working platforms are also better to resist rain and other inclement weather - helping to keep the contractor "out of the mud." Therefore, the soil strength improvements from LKD and SC fly ash at 4 hours after compaction were evaluated in this study. This early strength increase should not be confused with "soil stabilization." Soil stabilization involves long-term strength gains - typically measured at 7 to 28 days after compaction. Lime products and SC fly ash are also effective for long-term soil stabilization, but the focus of this study was rapid soil improvement for the construction site. Both chemical agents rapidly improve the CBR properties of the soil. For these soils, on average, the LKD increased the CBR by 4%, while the SC fly ash increased the CBR by 22%. LKD caused a significantly larger amount of rapid improvement in soil strength than did the SC fly ash. On average, LKD rapidly increased the CBR of the untreated soil more than twice as much as did the SC fly ash Untreated Soil % LKD % SC Fly Ash CBR Figure When choosing lime products or SC Fly Ash for improving the soil at the construction site......either can be used, but don't expect comparable results for similar amounts of material. These laboratory results are clear--lime or lime kiln dust is more effective than SC fly ash for soil drying, plasticity reduction and rapidly increasing the soil strength. The information in this publication is intended for the use of personnel competent to evaluate it. The characteristics of the soil tested are not necessarily the same as the characteristics of other soils. Any technical advice furnished is believed to be reliable, but Carmeuse makes no warranty regarding such advice. The implied warranties of merchantability and fitness for a particular purpose are expressly disclaimed. The user of this information releases Carmeuse from any liability arising out of the use of this information. Lime...the proven solution

6 More than just a lime supplier, Carmeuse offers valuable technical support to the construction industry Since our entry into the soils market in 22, we have developed a close working relationship with many customers that extends beyond the typical lime supplier relationship. Specifically, we have assisted many customers with technical issues including: Responding to technical problems and inquiries such as - Pavement design - Materials and mixtures - Specifications and standards - Construction - Quality assurance Professional presentations at seminars, conferences and local meetings Conducting educational sessions on soil stabilization in specifiers offices Assisting with field construction issues Conducting limited soils testing to evaluate the benefits of lime products Carmeuse Lime & Stone -- North America Operations For more information about a Carmeuse Location near you you call: Carmeuse Lime & Stone 11 Stanwix Street, 11th Floor Pittsburgh, PA 1222 Phone: / Fax: salesinfo@carmeusena.com Internet: Dolomitic Lime High Calcium Lime Industrial Sands Hydrator Terminal with Hydrator Limestone Terminals