Calcium nitrite as a corrosion inhibitor is mainly used to protect steel reinforcement in concrete by reducing its corrosion rate. Hence the effectiveness of calcium nitrite depends on its availability as a free nitrite in the pore solution. The present research work aims to determine the concrete mixture component mostly responsible for nitrite binding in concrete. Firstly, the experimental program included testing of nitrite binding in cement paste. Secondly, the effect of adding the fine aggregate (mortar mix) on nitrite binding was assessed. Finally, the mix with coarse aggregate (concrete mix) was evaluated. In-situ leaching method was used to obtain the pore solution that was needed. Measurement of pore solution with the In-situ leaching method and after an average of 48 days showed that concrete specimens have the most nitrite binding capacity. Then, the binding of nitrite was less in mortar and paste specimens respectively. Therefore, concrete specimens bind more nitrite compared to the paste and mortar specimens. The binding ratio increased whenever the nitrite addition level increased. Nevertheless, the free nitrite were similar in the case of the lowest nitrite addition for all types of mix. The pH levels for the mixes with nitrite present, were lower than those of the control mixes.

Master of Science / Department of Civil Engineering / Robert J. Peterman / As of 2005, 23% of the bridges in the Kansas infrastructure are classified as structurally deficient or functionally obsolete according to the ASCE Infrastructure Report Card (ASCE, 2008). One alternative to replacing the entire bridge structure is replacing only the superstructure with lightweight concrete. This option is more economical for city, county, and state governments alike. Replacing the superstructure with lightweight concrete can oftentimes allow the bridge rating to be upgraded to higher load capacities or higher traffic volumes. Furthermore, lightweight concrete can be used initially in a bridge deck to provide reduced weight and a lower modulus of elasticity, therefore lower cracking potential. The Kansas Department of Transportation is interested in the potential benefits of using lightweight aggregate concrete in Kansas bridge decks and prestressed bridge girders. This research project used three types of lightweight aggregate to develop lightweight concrete mixtures for a bridge deck and for prestressed bridge girders. Two of the lightweight aggregates were expanded shale obtained locally from the Buildex Company. One deposit was located in Marquette, Kansas, and the other in New Market, Missouri. The third lightweight aggregate source was expanded slate obtained from the Stalite Company in North Carolina. Aggregate properties including absorption, gradation, and L.A. Abrasion were evaluated. Over 150 lightweight concrete mixtures were created and tested and several mix design variables such as water-to-cement ratio, cement content, and coarse-to-fine aggregate ratio were evaluated. From these results, optimized bridge deck and optimized prestressed concrete mixtures were developed for each type of lightweight aggregate. Special concerns for lightweight aggregate concrete are addressed. These optimized concrete mixtures were then tested for KDOT acceptability standards for the concrete properties of compressive strength, tensile strength, modulus of elasticity, freeze-thaw resistance, permeability, alkali-silica reactivity, drying shrinkage, and autogenous shrinkage. All concrete mixtures performed satisfactorily according to KDOT standards. In addition, an internal curing effect due to the moisture content of the lightweight aggregate was observed during the autogenous shrinkage test.

Alkali-aggregate reaction (AAR) is one of the most harmful distress mechanisms affecting the durability and serviceability of concrete infrastructure worldwide. Currently, there is a need to forecast future behaviour of AAR-affected concrete, and thus analytical and numerical models have been developed over the years. Larive developed a model in 1998 that is able to describe the behaviour of concrete samples in the laboratory. This model has been widely accepted and used by AAR community, even to predict the behaviour of concrete structures in the field. Larive’s model is based upon three main parameters and although they are normally set according to the concrete type under analysis, these parameters do not have a clear physicochemical meaning to describe AAR-induced expansion and development. Furthermore, it is widely known that AAR is influenced by several measurable variables such as the type and reactivity degree of the aggregates, temperature, moisture, and alkali content; those are currently not accounted for in Larive’s equation. This work aims to incorporate the previously mentioned parameters to Larive’s equation so that AAR kinetics and final expansion might be precisely described in the lab and/or field. Results indicate that the proposed modified Larive’s equation can predict AAR kinetics and final expansion in the laboratory although some modifications seem still necessary to assess field structures.

One of the biggest challenges nowadays when dealing with critical AAR-affected infrastructure is to determine the induced expansion and damage attained to date in the different locations of the structure (i.e. diagnosis), to forecast its potential for further distress over time (i.e. prognosis), as well as its potential structural implications. There are a number of prognosis techniques that have been developed in the past decades which are currently being used worldwide. Yet, most of these approaches use residual expansion procedures based on accelerated laboratory tests performed on cores extracted from damaged structures. However, the majority of the results gathered from these tests have been found to be inaccurate when compared to the swelling behavior of the respective structure in the field and several potential issues have been raised with respect to the test setup and alkali leaching. This work aims to evaluate the efficiency of the various commonly used laboratory setups to assess the residual expansion of AAR-affected concrete. Three different setups (i.e. 38°C and 100% RH; 38°C and soaked in 1M NaOH and; 38°C and wrapped in 0.7M NaOH) and two types of reactive aggregates (fine and coarse) were selected for this research. Expansion is monitored over time and four damage degrees (i.e. 0.05%. 0.12%, 0.20% and 0.30%) are selected for further chemical, microscopic (DRI) and non-destructive tests. Results demonstrated that the 1 M NaOH protocol is much more aggressive than the other two setups. Furthermore, it provides the samples with a unique damage pattern that is different from field affected concrete. Finally, the proposed setup shows to be reliable in providing tested samples with similar deterioration mechanisms than expected. Yet, more efficiency in the reaction kinetics and understanding of the alkalis exchange from the system is still required.

We present an efficient algorithm for solving an interval coverage problem. Given n intervals of the same length on a line L and a line segment B on L, we want to move the intervals along L such that every point of B is covered by at least one interval and the sum of the moving distances of all intervals is minimized. As a fundamental computational geometry problem, it has applications in mobile sensor barrier coverage in wireless sensor networks. The previous work gave an O(n2) time algorithm for it. In this thesis, by discovering many interesting observations and developing new algorithmic techniques, we present an O(nlogn) time algorithm for this problem. We also show that Ω(n log n) is the lower bound for the time complexity. Therefore, our algorithm is optimal. Further, our observations and algorithmic techniques may be useful for solving other related problems.

published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

No description available.

This study was designed to measure the firm's capacity to produce more output from a given bundle of inputs. That is, the nature of economies of scale that obtains in the manufacturing industrial aggregate. The data on which this study is based was obtained primarily from two sources: (1) The Fourth National Development Plan (1981-85) of Nigerian Publication; and (2) The 1979 issue of the Yearbook of Industrial Statistics published by the United Nations.

The properties of prepacked concrete have long been studied and compared with those of normal concrete, although very little is known about its strength and deformation behaviour. Either by experiment or theory these aspects have been described in different ways. This thesis describes some experimental programmes on prepacked concrete that include its manufacture and a study of its strength, deformation and failure mechanism. To compare these aspects, normal concretes having the same water-cement and aggregate-cement ratios were made and tested under the same condition. The experimental work investigates the use of different types of admixture in grout in order to improve the strength of prepacked concrete. Among them the expanding admixture was found to be most suitable. Data are presented on some properties of grout using different types of admixture at various sand-cement ratios. Along with the strength investigation, investigation on modulus of elasticity, creep and shrinkage were also carried out. Tests of creep and shrinkage reveal that the magnitudes of both in prepacked concrete were much lower than in normal concrete. Different aspects of the failure mechanism of prepacked concrete are also presented and discussed.

Current Texas Department of Transportation (TxDOT) procedures for evaluating coarse aggregate for portland cement concrete (PCC) have been in place for over 39 years. Item 421 in the TxDOT "Standard Specifications for Construction and Maintenance of Highways, Streets, and Bridges" describes the tests and test limits that must be met by aggregates before they can be approved for use in portland cement concrete applications. The intention of Item 421 is to ensure that only strong, durable aggregates are used in concrete so that the life of concrete is not cut short by common distress mechanisms which ultimately lead to costly repairs and replacements. The two main tests currently used by TxDOT to evaluate aggregates are the magnesium sulfate soundness test and the Los Angeles abrasion and impact test. These tests are meant to characterize the overall soundness and resistance to abrasion and impact of an aggregate respectively. Unfortunately, past research has shown that the magnesium sulfate soundness and test and the Los Angeles abrasion and impact test are not able to successfully predict the field performance of an aggregate in concrete. The requirements of item 421 have thus far done a reasonably good job of ensuring long-lasting concrete; however the current tests and test limits may be unnecessarily precluding the use of some local materials. As high quality aggregate sources are depleted and transportation costs increase, it will become more necessary to distinguish good performers from marginal and poor performers in the future. If aggregate tests can be found that demonstrate better correlations with field performance, it may be possible to use more local aggregate sources and still provide the desired level of reliability for pavements, bridges, and other TxDOT concrete applications. Researchers are in the processing of collecting coarse and fine aggregates commonly used in Texas and testing these aggregates on a variety of alternative tests. Researchers will attempt to relate this test data to concrete behavior and ultimately recommend tests for improved TxDOT aggregate specifications. / text