Evaluating The Performance Of Controlled Low Strength Materials (CLSMs) Prepared Using Sulfate Spiked High Plasticity Clay

Abstract

When large scale civil engineering projects such as Integrated PipeLine (IPL) are to be constructed, several factors play a significant role in the successful completion of the project on time and on budget. With pipeline construction, one of the important tasks is excavation, with excavation comes the hauling of the excess excavated trench material to the disposal site. The hauling of unwanted excavated dirt from the site and bringing in select backfill material that meets the project requirements not only adds to the overall cost of the project but also raises concerns about sustainability. Transport of unwanted excavated materials require landfill space, contribute to air pollution by carbon emission from transport vehicles and also cause damage to pavements by the heavy loads being hauled. In order to account for cost as well as sustainability, Tarrant Regional Water District (TRWD) initiated a research study involving the reusability of in-situ native soil as bedding, haunch and backfill material for the IPL project. One part of the study involved the use of native soil treated with a stabilizer, cement, to prepare a flowable fill or Controlled Low Strength Material (CLSM). CLSM mix design using native soil not only cuts down cost of the hauling and bringing in select fill, it is also very effective when used as a utility bedding material. The proposed alignment of the IPL project underlines certain areas that contain expansive soil with elevated levels of sulfate concentration such as the Eagle Ford geological formation. Expansive soils with high levels of sulfates have been reported to be problematic all around Dallas/Fort Worth (DFW) metropolis. Sulfate induced heave has been a growing concern in the civil engineering projects employing calcium based stabilizers for soil treatment. This study focuses on the effects of using high sulfate expansive soil treated with cement in CLSM sample preparation. In order to achieve this goal, short term strength and long term durability studies were conducted on the samples which comprised of strength, volumetric and weight change and leachate studies. For the study, soil from Eagle Ford geological formation was selected and treated with Portland Cement (Type I/II). The five sulfate concentrations studied were 100 or less ppm (control soil), 2500 ppm, 5000 ppm, 10000 ppm and 20000 ppm. From the study, several significant conclusions were drawn. The analysis showed that soluble sulfates present in soil used for CLSM preparation do not have adverse effect on the 28-day cured unconfined compressive strength of the CLSM sample. This is in agreement with another study reported by the Japanese researchers who utilized recycled gypsum recycled to stabilize the soft clay soil and achieved acceptable Unconfined Compressive Strength (UCS) values (Kamei et al., 2011). The CLSM samples with elevated levels of soluble sulfate in the form of gypsum under short term strength exhibited higher UCS values. However, for the durability studies, the strength decreased significantly with increase in durability wetting-drying cycles. In addition, the increase in swell-shrink behavior of expansive soil with elevated levels of soluble sulfates was also distinctly reflected from the study when the same samples are subjected to durability cycles. Higher the concentration of soluble sulfates, higher the swell-shrink behavior exhibited by the CLSM which was evident by the samples failing before reaching 14 complete durability cycles. This confirms the effects of sulfates on the volume change and strength loss behavior of CLSM mixes. Furthermore, the study also showed increase in calcium ion leached out with the increase in sulfate concentration in the CLSM sample. This increase in cement loss could be the reason for the loss of strength of CLSM samples during durability studies.