Tyson Rupnow

Laboratory Investigation of the Effect of Mixed Nitrogen Dioxide and Nitrogen Oxide Gases on Titanium Dioxide Photocatalytic Efficiency in Concrete Pavements

Nitrogen oxides (NOx) emitted from vehicle exhausts are associated with adverse health effects on the public. Self-cleaning, air-purifying concrete pavement is a rapidly emerging technology that can be constructed by using a photocatalyst such as titanium dioxide (TiO2). The main objective of this study was to evaluate the environmental effectiveness of TiO2 coating in photodegrading mixed NO2 and NO gases from the atmosphere. Results of the experimental program determined that increasing the flow rate and NO2/NOx ratio negatively affect the effectiveness of the photocatalytic process. However, within the evaluated range, the titanium content and aggregate gradation had little effect on NOx removal efficiency. The highest photodegradation rate was observed at 25% relative humidity, which balances the availability of hydroxyl radicals at the surface with NOx contact with the photocatalytic surface.

Microencapsulation of Calcium Nitrate for Concrete Applications

The use of encapsulating healing agents that allow the self-healing of concrete has emerged as a potential solution to the current decay and costly maintenance of concrete infrastructure; however, many healing agents are expensive. The objectives of this study were to develop a procedure for the production of urea–formaldehyde microcapsules of calcium nitrate and to evaluate the effects of the microcapsules on self-healing efficiency in concrete. Calcium nitrate was selected for microencapsulation, given its low cost and its effect on acceleration of the setting of unhydrated cement. The results indicated that the agitation rate and the temperature had a linear correlation with the microcapsule diameter and the shell wall thickness, respectively. A higher agitation rate resulted in a smaller microcapsule diameter, whereas a higher temperature resulted in a thinner shell wall. The morphology of all microcapsules synthesized was virtually the same throughout the experimental matrix, with the shell walls of all the microcapsules observed having a smooth exterior surface and a rough interior surface. All microcapsules produced were also observed to have a broad particle size distribution. This characteristic was attributed to the type of surfactant used in the process. Analysis of the effects of the microcapsules on the self-healing efficiency of concrete showed that the modulus of elasticity increased after healing for all concrete specimens prepared with self-healing agents. The largest increase in the modulus of elasticity was observed at a microcapsule content of 0.50%. The results also showed that concrete specimens into which microcapsules were incorporated at any concentration had greater surface resistivities than control specimens.

Effect of Self-Healing Calcium Nitrate Microcapsules on Concrete Properties

Self-healing concrete with microencapsulated calcium nitrate was investigated. The compressive strength of concrete admixed with microcapsules (as a percentage of the weight of the cement) was tested and compared with that of control specimens of the same mix design without microcapsules. Surface resistivity tests were conducted to quantify the surface permeability of the concrete specimens with and without microcapsules. The self-healing potential was measured by the modulus of elasticity test (ASTM C469), with measurements being taken before and after damage after 14 days. After the concrete was damaged by application of 80% of its ultimate load, all specimens were incubated by immersion in water. The results showed that the concentration of microcapsules added and the size of the microcapsules had a direct impact on the compressive strength of the concrete. Furthermore, the concrete specimens into which microcapsules were incorporated had greater surface resistivity than the control specimens. The recovery of the modulus of elasticity was analyzed according to the increase from the modulus of elasticity recorded after application of 80% of the sample’s ultimate load and the increase relative to the initial modulus of elasticity of the concrete in the virgin state. Overall, the results of this study indicated that although microcapsules caused a decrease in the compressive strength of the concrete, they enhanced the self-healing capability of the concrete that was produced. To take advantage of the benefits of microcapsules, the authors recommend that future work evaluate the use of a dispersing agent to reduce the amount of microcapsules needed in the mix.

Development of Precision Statement for Concrete Surface Resistivity

Seventeen surface resistivity meters and 17 operators participated in the round-robin testing conducted at the Louisiana Transportation Research Center over 2 days. The tests were conducted side by side, and the individual meters results were compared. Eight mixtures representing multiple permeability classes were tested with two replicates for each mixture. A precision statement was developed for use with Louisiana Department of Transportation and Developments TR 233, Surface Resistivity Indication of Concretes Ability to Resist Chloride Ion Penetration. The single operator coefficient of variation (CV) of a single test result has been found to be 2.2%. Therefore, the results of two properly conducted tests by the same operator on concrete samples from the same batch and of the same diameter should not differ by more than 6.2%. The multilaboratory CV of a single test result has been found to be 3.9%. Therefore, the results of two properly conducted tests in different laboratories on the same material should not differ by more than 11%.

Surface Resistivity Measurements Evaluated as Alternative to Rapid Chloride Permeability Test for Quality Assurance and Acceptance

ASTM C1202 tests were conducted at various ages with the corresponding surface resistivity test, and the results were compared. Samples tested included field- and laboratory-prepared samples. The laboratory test matrix tested several mixtures common to Louisiana at a wide range of ratios of water to cementitious materials (w/cm) to evaluate the range of the surface resistivity meter. The surface resistivity measurements correlated well with rapid chloride permeability measurements across a wide range of permeability values and sample testing ages. Suitable correlations were found between both the 14-day and the 28-day surface resistivity values and the 56-day rapid chloride permeability values. The variability of the surface resistivity test results is usually less than the variability of the rapid chloride permeability test results. The surface resistivity meter was also able to identify great differences in w/cm ratios for the same mixtures. The surface resistivity meter was determined to be user friendly. The preliminary cost–benefit analysis showed that implementation of the device would save the department about

Investigation of Portland Cement Concrete Mix Consistency and Concrete Performance Using a Two-Stage Mixing Process

101,000 in personnel costs in the first year. It is estimated that contractors would save about

Laboratory Evaluation and Field Construction of Roller-Compacted Concrete for Testing Under Accelerated Loading

1.5 million in quality control costs. The cost–benefit ratio for this project is estimated to be about 15. A Louisiana Department of Transportation and Development test requirements procedure, TR 233, has been developed and implementation of the surface resistivity device has begun.

Impact of Mixed Nitrogen Dioxide (NO2) and Nitrogen Oxide (NO) Gases on Titanium Dioxide Photodegradation of NOx

The objective of this study was to investigate the effects of different mixing processes, particularly a two-stage mixing process, on fresh and hardened characteristics of pastes and concrete. Characteristics studied for pastes included rheological effects (i.e., yield stress, thixotropy, viscosity, and peak stress) and compressive strength for mixes prepared in a Hobart mixer and a high-shear mixer. Parameters measured for the concrete study included fresh concrete air and slump, compressive strength, and hardened concrete air void characteristics. The paste study results show that for increased mixing time, the compressive strength is not significantly influenced. The rheology results show that longer mixing times with a high-shear mixer lead to lower viscosity, thixotropy, and peak stress; this indicates better-mixed slurry when compared with a shorter mixing time and the Hobart mixer. The fresh concrete made with the two-stage mixing process shows reduction in air content, and the hardened concrete sh...

Evaluation of Self-Healing Concrete with Microencapsulated Calcium Nitrate

The Louisiana Department of Transportation and Development has seen a rapid decline of low-volume roadway serviceability in recent years as a result of oil and gas exploration within the Fayetteville Shale Play near Shreveport, Louisiana. Similar results are expected on the low-volume roadway network within the Tuscaloosa Shale Play, north of Baton Rouge, Louisiana, as exploration expands. The objectives of this research were to determine appropriate proportions of roller-compacted concrete mixture for the construction of accelerated loading test lanes and to document field construction activities. Concrete samples were produced with four cement contents to determine the effect of moisture and density; the samples were tested for compressive strength at 7 and 28 days of age. The field testing included nuclear density testing, thickness measurements, and field-prepared compressive strength specimens. A walking profiler was used to determine the international roughness index (IRI). All laboratory-produced mixtures exceeded a compressive strength of 4,000 pounds per square inch (psi). When the desired surface characteristics and density were considered, 450 lb/yd3 was chosen as the minimum cementitious content for the construction of the test lanes. The field construction results showed that the speed of construction affected the density, the IRI, and the surface characteristics. An increased speed of construction yielded a rougher surface texture (an increased IRI between 360 and 620 in./mi) and slightly lower densities. The compressive strengths were still adequate and exceeded 4,500 psi at 28 days old. On the basis of the field results, IRI values in the 100- to 130-in./mi range and compressive strengths exceeding 5,000 psi may be expected in a full-scale roadway construction effort.

Investigation of Factors Affecting PCC Surface Resistivity through Ruggedness Testing

Nitrogen oxides (NOx) emitted from vehicle exhausts are associated with adverse health effects on the public. Self-cleaning, air-purifying concrete pavement is a rapidly emerging technology that can be constructed using photocatalyst such as titanium dioxide (TiO2). The main objective of this study was to evaluate the environmental effectiveness of TiO2 coating in photodegrading mixed NO2 and NO gases from the atmosphere. Results of the experimental program determined that increasing the flow rate and NO2/NOx ratio negatively affect the effectiveness of the photocatalytic process. However, within the evaluated range, the titanium content and aggregate gradation had little impact on NOx removal efficiency. The highest photodegradation rate was observed at 25% relative humidity, which balances the availability of hydroxyl radicals at the surface with NOx contact with the photocatalytic surface.