Evaluation of the Performance and Cost-Effectiveness of Engineered Cementitious Composites (ECC) Produced from Region 6 Local Materials

The project objective is to develop cost-effective Engineered Cementitious Composites (ECC) with locally available ingredients in Region 6 to address the deficiencies observed in ordinary concrete materials. The study explored the utilization of two types of river sands (coarse and fine), two types of PVA fibers (long and short), four levels of cement replacement with Class F fly ash, and the implementation of recycled crumb rubber in the performance of ECC materials. A total of 24 mix designs were prepared and evaluated in compression, tension, and bending to assess its mechanical properties. Furthermore, the cracking characteristics of the materials produced were evaluated to assess the durability potential of these composites. Lastly, the cost of each mix design and the feasibility of ECC implementation in transportation infrastructure were assessed. The experimental results showed that implementing crumb rubber and/or increasing contents of fly ash in the mixtures produced a positive impact in the ductility of the materials. However, a tradeoff between ductility and strength was observed. Furthermore, the utilization of the different types of sand evaluated in this study produced minor effects in the mechanical properties of ECCs evaluated. The properties of the materials developed in this study were exceedingly superior than that of regular concrete. It was concluded that ECC materials are promising for the future of transportation infrastructure

Self-Healing Concrete using Encapsulated Bacterial Spores in a Simulated Hot Subtropical Climate

Bacterial concrete has become one of the most promising self-healing alternatives due to its capability to seal crack widths through microbial induced calcite precipitation (MICP). In this study, two bacterial strains were embedded at varying dosages (by weight of cement) in concrete. Beam specimens were used to identify the maximum crack-sealing efficiency, while cylinder samples were used to determine their effects on the intrinsic mechanical properties, as well as its stiffness recovery over time after inducing damage. The concrete specimens were cured in wet-dry cycles to determine their feasibility in Region 6. The results showed that the specimen groups with the highest calcium alginate concentrations (including the control specimens with embedded alginate beads but no bacteria) resulted in higher increases in stiffness recovery. Similarly, the beam samples containing alginate beads (also including the Control 3%C specimen group) had superior crack-healing efficiencies than the control samples without alginate beads (Control NC). This was attributed to the fact that the alginate beads act as a reservoir that can further enhance the autogenous healing capability of concrete. Overall, further research is recommended to verify whether the promising results reported in the literature (relating to self-healing mortar) correlate with concrete proportionally. In addition, there is a need to explore the factors that can maximize the self-healing mechanism of bio concrete through MICP, whether an alternative encapsulation mechanism, nutrient selection, curing regime, or bacterial strain is desired

Evaluation of laboratory and field techniques to improve portland cement concrete performance

This dissertation is presented as a compilation of five papers. Each paper is presented as a chapter in the dissertation and includes a short literature review, research data, significant findings, and references. A general conclusion section follows the main body of the dissertation and summarizes the significant findings and includes recommendations for further research.;The first paper presents a paste and concrete laboratory study investigating the two-stage mixing process and its effects on portland cement concrete mix consistency and concrete performance. In the paste study, mixing energy was varied to determine the effects on rheological and compressive strength properties. The concrete study investigated the two-stage mixing process and its effects on fresh and hardened concrete properties.;The second paper details a new characterization procedure for portland cement using the heat signature. A Type I/II portland cement was used to determine the effects of initial water and initial cement temperature on the heat signature of the paste. Several other portland cements, including blended cements, were also investigated to show the differences in cement chemistry when comparing the heat generation curves.;The third paper investigates the effects of differing air entraining agent, water reducing agents, and supplementary cementitious materials on the air void structure of fresh mortar samples. The air void analyzer was used to document the air void structure and identify anomalies or incompatible material combinations. Cubes were cast for compressive strength testing at seven days to show incompatible combinations in terms of retarded strength gain.;The fourth paper uses AVA data from a sixteen state pooled fund study to evaluate the AVA sampling locations. Samples were obtained from the slip formed concrete surface on vibrators and between vibrators from sixteen states. AVA samples were obtained before the paver on three states. Statistical analysis (t-test) was conducted at an alpha level of 0.05 to determine significance.;The fifth paper presents data on the heat signature of ternary mixes. The heat signatures were characterized and the results were modeled using slope 1 and slope 2, maximum temperature, time to maximum temperature, area under the heat signature curve, initial set, and final set.</p

Influence of subgrade improvement and non-uniformity on pavement performance

This thesis contains results from three projects describing self-cementing fly ash stabilization of RAP-soil mixtures, stabilization of limestone screenings for use as a structural layer in road construction, and finite element modeling results of various subgrade materials including self-cementing fly ash stabilized subgrade, natural subgrade, granular subbase, and hydrated fly ash. The first project shows that self-cementing fly ash stabilization of RAP-soil mixtures is economically feasible and structurally capable of supporting construction traffic. The increase stiffness from the addition of self-cementing fly ash increases capacity ensuring long term pavement performance. Addition of self-cementing fly ash increases the consolidated shear strength about five times. The second project shows construction operations and field results proving that stabilization of limestone screenings is viable, cost effective, and produces an adequate structural layer for road construction. The measured moisture-density curves for manufactured sand and limestone screenings are about the same, and the moisture-strength curves show a dramatic decrease in strength beyond the optimum moisture content for strength. Durability testing concluded that CKD stabilized manufactured sand and limestone screenings are not viable construction alternatives, and the addition of class C fly ash with CKD significantly increased the durability of the mixtures. The third project concluded that a link exists between subgrade non-uniformity and pavement performance. Field testing, with the DCP, Clegg Impact Hammer, nuclear density gauge, and GeoGauge, and statistical analysis of subgrade materials concluded that granular subbase, self-cementing fly ash treated subgrade, and HFA decrease the variability of field results. Finite element modeling analysis proved that a link exists between subgrade non-uniformity and pavement performance. Uniform modeling conditions produced lower average deflections and stresses increasing pavement life. Statistical analysis concluded that modeling uniform subgrade conditions produce average stresses that have less variability than those for non-uniform modeling conditions. Pavement response reliability increased with the addition of uniform subgrade, proving that subgrade non-uniformity influences pavement performance.</p