C. Vipulanandan

Impedance Spectroscopy Characterization of a Piezoresistive Structural Polymer Composite Bulk Sensor

In this study, self-monitoring characteristics of a new piezoresistive structural polyester polymer composite bulk sensor were investigated under various loading conditions using impedance spectroscopy (IS). IS was used to estimate the bulk resistance of the piezoresistive polymer composite and the contact resistance of the two-probe measuring system used, along with the stress and shape dependence of these resistances. The piezoresistive behavior of cylindrical specimens in compression and circular disk specimens in bending and splitting tension showed repeatable characteristics. The contact resistances were about 1 % and 4.4 % of the bulk resistances for the cylindrical and circular disk specimens, respectively. The contact resistances were relatively small compared to the bulk resistances, and the change in contact resistance with applied stress was quantified. The average piezoresistivity coefficient for cylindrical specimens was 0.015 MPa−1 in compression, and for the circular disk specimens the coefficients were 3.1 × 10−4 MPa−1 and 4.62 × 10−4 MPa−1 under bending and splitting tensile loading, respectively. An incremental stress-resistivity model was used to predict the observed behavior of the piezoresistive polymer composite.

Stress-Strain Behavior and California Bearing Ratio of Artificially Cemented Sand

In this study, effects of cement content and curing time on the compressive stress-strain relationship and California bearing ratio (CBR) value of artificially cemented sand cured up to 7 days was investigated. The CBR study was focused on investigating the sensitivity of this non-destructive test to measure the changes in the compacted cemented sand properties during construction (limited curing time). The cement content in the cemented sand was varied up to 6 % by weight. The strength, modulus, and unit weight of the artificially cemented sand varied from, 60 to 1250 kPa, 14 to 290 MPa, and 15.98 to 18.33 kN/m3, respectively. The CBR values for cemented sand, compacted using the standard proctor method, varied from 8 to 230 %. Compressive stress-strain relationship of cemented sand was represented by a non-linear relationship. Relationship between compressive properties of cemented sand and the CBR was also investigated. The variation of compressive strength, modulus, and CBR values with curing time were represented using hyperbolic relationships. Finite element method (FEM) was used to model the CBR test, based on the data obtained from the unconfined compression tests for 1.5, 3, and 6 % cemented sand. In the FEM analyses the cemented sand was modeled using linear elastic-perfectly plastic constitutive relationship with Mohr-Coulomb failure criteria. The ratio of predicted to measured CBR values varied from 0.67 to 1.31.

Fracture Behavior and Digital Image Correlation (DIC) Characterization of Multilayered Polymer Insulation Composite Coating Used in Subsea Pipelines

In this study, fracture and failure behavior of multilayered polymer composite used as thermal insulator in subsea pipe line was investigated at various strain rates (e) with and without simulated cracks. For this study, polymer composites samples were obtained from field pipes used in the North Sea. The multilayered polypropylene composite materials were tested in four-point bending with and without notch at various displacement rates. Also the fracture behavior of the polymer composite materials was investigated in direct tension at various loading rates with and without pinholes. A three dimensional (3D) digital image correlation (DIC) system was used to monitor the deformation field near the crack tip, which provided the strain field distribution with the crack initiation and growth with time. The polymer composite material was viscoplastic and the tensile strength and failure strain increased and decreased respectively with the increasing strain rate. The tensile strain intensity factor γ (a new concept) was determined to govern the fracture behavior of the materials due to the strain concentration at the crack tip. In the range of strain rates (e) investigated in this study, the strain intensity factor γ was over 30 for the unfilled polypropylene (PP) and polypropylene composite with 65% glass filler.

Leak Control in Wastewater Lateral Joint Using a Polymer Grout

The EPA estimates that major increase in inflow and infiltration (I/I) is caused by the leaking residential laterals. Several types of grout materials have been used in controlling I/I problems in wastewater systems and storm systems. In this study, a test protocol was developed by the Center for Innovative Grouting Materials and Technology (CIGMAT) and was approved by the USEPA to evaluate the performance of polymeric grout used in the rehabilitation of lateral joints in wastewater facilities and to quantify the infiltration at pipe joints using a combination of model and laboratory tests. The polymer grout was used to control the leak of over 1000 gallons/day at a leaking lateral joint. For the leaking joint model test, 203 mm (8”) diameter leaking pipe joints were used in soil box. The grout used in this study was characterized using the working, physical, mechanical and durability properties. It was observed that, the polymeric grout which had a gelling time of 24.5 seconds, was impervious to water when grouted in soil when the hydraulic gradient was 100. The durability test results showed that, the grouted sand was extremely resistant to varied chemical environments and the strength deterioration was negligible for a period of one month. The grout was effective in reducing the discharge from over 1000 gpd (4940 liter/day) to zero at hydraulic pressures of 3, 4 and 5 psi (21 to 35 kPa). The large scale model test was simulated using a numerical finite element model which predicted the results well.

Field Evaluation of A New Down-Hole Penetrometer (DHP-CIGMAT)

Drilled shafts are increasingly used as foundations to support bridges and transportation structures in geomaterials such as soft-rocks and hard clay. Locating the bottom of the borehole during construction with the required strength is critical. Hence developing a simple device that could be easily adapted/used with the drilling tool was of interest in this study. Determining the shear strength of the geomaterial in the borehole and at the bottom of the borehole can lead to better quality control of construction by identifying the various layers based on strength. In this study, a down-hole penetrometer (DHP-CIGMAT) was designed, built and tested to determine its effectiveness in measuring the strength of soil/soft rock. Based on limited field tests, linear correlations between geomaterial strengths and DHPCIGMAT deflection have been developed. Finite element analysis was used to verify the DHP-CIGMAT test results.