Charles E. Pierce

Potential of scrap tire rubber as lightweight aggregate in flowable fill

Flowable fill is a self-leveling and self-compacting material that is rapidly gaining acceptance and application in construction, particularly in transportation and utility earthworks. When mixed with concrete sand, standard flowable fill produces a mass density ranging from 1.8 to 2.3 g/cm(3) (115-145 pcf). Scrap tires can be granulated to produce crumb rubber, which has a granular texture and ranges in size from very fine powder to coarse sand-sized particles. Due to its low specific gravity, crumb rubber can be considered a lightweight aggregate. This paper describes an experimental study on replacing sand with crumb rubber in flowable fill to produce a lightweight material. To assess the technical feasibility of using crumb rubber, the fluid- and hardened-state properties of nine flowable fill mixtures were measured. Mixture proportions were varied to investigate the effects of water-to-cement ratio and crumb rubber content on fill properties. Experimental results indicate that crumb rubber can be successfully used to produce a lightweight flowable fill (1.2-1.6 g/cm(3) [73-98 pcf]) with excavatable 28-day compressive strengths ranging from 269 to 1194 kPa (39-173 psi). Using a lightweight fill reduces the applied stress on underlying soils, thereby reducing the potential for bearing capacity failure and minimizing soil settlement. Based on these results, a crumb rubber-based flowable fill can be used in a substantial number of construction applications, such as bridge abutment fills, trench fills, and foundation support fills.

Cement Kiln Dust in Controlled Low-Strength Materials

This paper examines the fluid and hardened state properties of controlled low-strength materials (CLSM) with cement kiln dust (CKD) as the primary binding agent. The low-strength property of CKD can be advantageous when used in CLSM as most applications require future excavatability. Because CLSM is often produced with fly ash (FA), it inherently mitigates the higher water demand of CKD. Lab-prepared mixtures with CKD:FA ratios of 1:12, 1:6; and 1:1 were studied by varying the water-binder ratio (w/b) from 0.95-1.10. Flowability, volume stability (bleeding), setting time, mass density, and 28-day unconfined compressive strength (UCS) were measured for each mixture. Results reveal that high flowability and setting times within 24 hrs could be achieved with most mixtures, although the bleeding levels are higher than normal. 15 CKD-CLSM mixtures were proportioned to produce average strengths ranging from 34-460 kPa. The wide range of strengths is significant for 2 reasons: 1) all mixtures are considered to be excavatable based on these 28-day strengths; and 2) stress-strain behavior of these mixtures is representative of soil types ranging from soft to very stiff clays. Thus, cement kiln dust can be beneficially added to produce a very low-strength material that offers comparable strengths to soils used for conventional fills and many other low-strength applications.

LONG-TERM STRENGTH DEVELOPMENT OF CONTROLLED LOW-STRENGTH MATERIAL

This paper presents results of an experimental study conducted to evaluate the combined effects of prolonged mixing time, late water inclusion, and variations in total water content on the long-term compressive strength of controlled low-strength material (CLSM). Long-term strengths refer to strengths measured after 600 days of curing. To evaluate strength development in moist ground conditions, sampled specimens were continuously cured in water. The main aim of the research was to determine the effects of mixing and water content variables on the long-term strength development of the immersed CLSM mixture as measured by unconfined compression testing. Findings are discussed.

Methods for Field and Laboratory Measurement of Flowability and Setting Time of Controlled Low-Strength Materials

Flow consistency and setting time are two important properties of controlled low-strength materials (CLSM). This paper describes and evaluates several standard and non-standard methods to measure these properties. Several mixtures with a range of water-to-binder ratios were investigated through a series of field and laboratory experiments. A linear relationship was observed between the flowability measured by the flow cylinder method (ASTM D 6103) and the inverted slump cone method. Pocket penetrometer and Torvane measurements were compared to the Kelly Ball method (ASTM D 6024) for estimating sufficient bearing capacity. Pocket penetrometer resistance correlates well, but its capacity was often exceeded. Volume stability should be controlled to avoid softening of the surface and subsequent delays in measured hardening time.

Effects of Multiple Crimps and Cable Length on Reflection Signatures from Long Cables

The accuracy of time domain reflectometry (TDR) measurements of rock shearing with cable lengths greater than 60 m has not been adequately documented. This paper presents the results of controlled crimping and shearing of a 530 m long, 22.2 mm diameter coaxial cable for comparison with theory and the existing data from cables up to 60 m long. Effects of both single and multiple deformities along transmission lengths of 94, 268, and 530 m were investigated. The Northwestern University TDR Signature Analysis (NUTSA) program was employed to track and analyze reflection spikes in the waveforms produced by controlled deformation. The results show that pulse attenuation has a significant effect on signal reflections. Reflection amplitudes were reduced by 500% as cable length increased from 94 m to 268 m. Signal reflections produced by downstream deformations are slightly decreased (amplitude reduction < 1 m n single or multiple deformations are applied upstream on the cable. Deformation-reflection relationships can be characterized as bi-linear or exponential, and show that shear deformation can be effectively correlated with TDR reflection amplitude at distances up to 268 m.

Environments for fostering effective critical thinking in geotechnical engineering education (Geo-EFFECTs)

This paper describes the development, implementation, and assessment of instructional materials for geotechnical engineering concepts using the Environments for Fostering Effective Critical Thinking (EFFECTs) pedagogical framework. The central learning goals of engineering EFFECTs are to (i) improve the understanding and retention of a specific set of concepts that provide core knowledge and (ii) encourage students to recognise and develop critical thinking skills that lead to growth in engineering judgement. The practice of geotechnical engineering deals with complex and uncertain soil conditions, where critical thought and judgement are imperative. Three geo-EFFECTs were created in the context of levee reconstruction, levee permeability, and settlement of a tower structure. Students often provided inaccurate estimates to driving questions set in those contexts; when given opportunities for self-exploration and self-correction in the EFFECT structure, students often achieved more accurate final solutions. Overall, results suggest that EFFECTs have a measurable, positive impact on student learning.

Measurement of water pressure and deformation with time domain reflectometry cables

Time domain reflectometry (TDR) techniques can be deployed to measure water pressures and relative dam abutment displacement with an array of coaxial cables either drilled and grouted or retrofitted through existing passages. Application of TDR to dam monitoring requires determination of appropriate cable types and methods to install these cables in existing dams or during new construction. This paper briefly discusses currently applied and developing TDR techniques and describes initial design considerations for TDR-based dam instrumentation. Water pressure at the base of or within the dam can be determined by measuring the water level within a hollow or air-filled coaxial cable. The ability to retrofit existing porous stone-tipped piezometers is an attractive attribute of the TDR system. Measurement of relative lateral movement can be accomplished by monitoring local shearing of a solid polyethylene-filled coaxial cable at the interface of the dam base and foundation materials or along adversely oriented joints. Uplift can be recorded by measuring cable extension as the dam displaces upward off its foundation. Since each monitoring technique requires measurements with different types of coaxial cables, a variety may be installed within the array. Multiplexing of these cables will allow monitoring from a single pulser, and measurements can be recorded on site or remotely via a modem at any time.

Ground Damage Assessment from Tornado-Borne Projectiles

Tornados often create and transport large amounts of debris that can be ejected at high velocities. There have been empirical and theoretical studies conducted on missile transport and impact, but ground damage from tornado-borne projectiles has not been well documented in the field. This paper summarizes the evidence and extent of ground damage from tornados and proposes a method for field data acquisition and assessment. Impact velocities of projectiles can be estimated using field measurements of ground deformations coupled with projectile and soil properties. Ground damage has the potential to adversely affect subsurface infrastructure if the penetration is deep enough to strike a buried pipeline or if the ground impact transfers sufficient energy to induce local settlement around a buried pipeline. With reliable data, ground damage assessment can be considered for inclusion as part of the Enhanced Fujita Scale for tornado classification.

Durability of Chemically Treated Plastic Soil for Unpaved Roads

Unpaved roads are subject to rapid deterioration and large deformations under mechanical and environmental stresses that can render them impassable. Prior work has shown that plastic soils can be mixed with a polymeric chemical admixture to create a hydrophobic material and potentially minimize these issues. The purpose of this work is to assess the durability of a low plasticity clay soil treated with a chemical admixture by evaluating changes in physical and mechanical behavior when subjected to alternating cycles of wetting and drying. Volumetric change, water content change, and mass loss were measured at the completion of each one of up to twelve wetting and drying cycles. Unconfined compression tests were performed after select cycles to assess changes in mechanical properties. Tests were also performed on specimens stabilized with Type I/II portland cement for comparison. It was found that the specimens with chemical admixture treatment survived a full twelve cycles of wetting and drying. The volume changes of the specimens were small (±2 %) and there was no apparent reduction in strength. The chemically stabilized soil retained its physical and mechanical properties in a manner comparable to cement stabilization of the same soil. These results suggest that the CAT produces a sufficiently stable material when subjected to alternating wetting and drying conditions and has potential applications in improving long-term performance of unpaved roads.

TDR-Based Shear Deformation Measuring System for Slope Failure Modeling

Physical soil models are often used to study slope failure in centrifuge and/or shaking table tests. An important part of such physical modeling is to monitor the subsurface deformation patterns of failing slopes. As an emerging technology to monitor internal deformation of geo-materials, time domain reflectometry (TDR) has been successfully applied in field monitoring of unstable slopes. This paper presents the development of a custom-made TDR sensor and its application in a 1-g slope failure model test. The test results show that the TDR system is capable of capturing localized shear deformation in small soil models. Trial studies of using the TDR system in centrifuge and shaking table experiments demonstrate that the system has the potential of being successfully applied in centrifuge and shaking table testing.