Graduation date: 1999

The Environmental Conditioning System (ECS) was designed to evaluate the water sensitivity of asphalt concrete mixtures. The ECS subjects asphalt concrete specimens to a series of conditioning cycles including water flow, elevated and/or lowered temperature, and repeated axial loading. The purpose of this research was to: (1) evaluate the ECS test apparatus and procedure, and (2) determine whether the ECS can identify asphalt concrete mixtures that will perform well, or poorly, in the field with regard to water sensitivity. Twelve primary field test sections were identified. For each section, specimens were prepared in the laboratory using the original mix design (or the mix design identified by extraction), and the original aggregates, asphalts, and admixtures. Specimens were tested using two procedures: the ECS and the Oregon State University (OSU) wheel tracker. Field cores were used to evaluate in-situ mixture performance. Nine additional mixtures that have historically experienced water damage were tested in a limited secondary test program. Analyses were performed to determine the mixture properties that were significant in the prediction of mixture performance in the ECS. Mixture type was consistently the most significant predictor of ECS modulus ratio (change in mixture stiffness), degree of visual stripping, and binder migration, which were the performance indicators for water sensitivity evaluated in the ECS. Additional analysis indicated the existence of correlations among the ECS response variables. Significant correlations were found between the coefficient of water permeability and the degree of visual stripping; and between specimen deformation and the degree of visual stripping and binder migration. Mixture performance was compared between the ECS and the OSU wheel tracker and the field. Results indicate that the ECS test procedure can distinguish the relative performance of mixtures, with regard to water sensitivity, and mixture performance in the ECS correlates well with performance in the OSU wheel tracker. No correlation was found between mixture performance in the ECS and mixture performance in the field for the primary test sections. However, the primary field sections are relatively young, and water damage is expected to manifest itself in the future in those pavements identified as water sensitive by the ECS. The ECS predicted failure in the secondary mixtures which were identified as having had poor performance with regard to water sensitivity. / Graduation date: 1994

Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2006. / Includes bibliographical references (leaves 126-133). Also available in electronic version.

This PhD thesis is divided into two parts. Part one dealswith the development of the material and the mechanicalproperties of Steel Fibrous Cement Based Composites (SFCBC) forimproving bridge design and construction. It familiarizes thehydration mechanisms of the high performance concrete with thehelp of Powers´ and Jensen´s models. Concretes withdifferent water-cement ratio were compared with each other withrespect to degree of hydration and hydration products. Thisanalysis showed that high performance concrete has higherstrengths not because it has more gel solid, but due to ithaving less porosity and higher filler content compared toordinary concrete. A number of experiments were performed to achieve a mixdesign method for a SFCBC, which has good workability, highearly and long-term strength and good durabilitycharacteristics. A Self-compacting and self-leveling fibrouscomposite, which has ultra high strengths (Compressive strengthfc= 180 ~ 220MPa and flexural tensile strengthfföi= 14 ~ 32MPa depending on the volumefraction of fibers) was produced. This composite was alsotested under different curing conditions in order toinvestigate the effect of curing on hydration andself-desiccation shrinkage. These tests showed that SFCBCshould not be water-cured under a long period andself-desiccation influences the compressive strengthnegatively. Test of scaling at freezing showed that SFCBC hasvery good durability characteristics. Part two deals with the behavior of SFCBC in the anchoragezones of prestressed bridges. The prismatic composite specimenswere tested for different volume fractions of fibers underdifferent concentrations ratios of strip loading. The resultsof these tests showed that the ultimate strength of the SFCBCspecimens was approximately twice that of ordinary concretewith the same size (fc= 60MPa reinforced with stirrups). Therefore,SFCBC has good possibility to replace the traditional rebars inthe anchorage zones of prestressed bridges. This composite has different behavior than the traditionalconcrete e.g. crack formation, failure criteria, effectivestrength and angle of friction. A vertical crack on thecenterline was occurred while wedge developed under the loadingplate. In contrast to ordinary concrete, the cracks could notreach to the bottom of the blocks. The tests results gave the ideas of that this material actslike metals or plastics in the high fiber content. Thismaterial is neither very brittle as concrete nor very ductileas metals but it is somewhere between them. Upper-bound plasticity solutions were utilized for modelingthe bearing capacity of SFCBC. Predictions of this method aregood enough to estimate the bearing capacity of SFCBC in theanchorage zones of prestressed bridges. <b>Keywords:</b>Process improvement of bridges, Prestressedconcrete, High performance concrete, Ultra high performanceconcrete, Hydration, Cement based composites, Fibers,Self-compacting concrete, Bearing capacity, Anchorage zones,Tests

Most materials including concrete have pre-existing flaws or defects. The fracture energy of concrete is a basic material property needed to understand fracture initiation and propagation in concrete. Whether fracture energy is size dependent or not is being discussed world over. Strictly the fracture energy if taken as a material property should be constant, and should be independent of the method of measurement, test methods, specimen shapes and sizes. A computational study on simulation of fracture in concrete using two dimensional lattice models is presented. A comparison is made with acoustic emission (AE) events with the number of fractured elements. A three-point bend specimen (TPB) is modeled using regular triangular lattice network. It was observed that the number of fractured elements increases near the peak load and beyond the peak load. AE events also increase rapidly beyond the peak load. Singular Fractal Functions (S.F.F) has been employed to interpret the size effect of quasi-brittle materials like concrete. The usual size dependent fracture energy of High Strength Concrete (HSC) beam is reported. The results are presented which are obtained directly from the experiments related to size effect in concrete carried out in the Structural engineering laboratory, Department of Civil engineering, IISc. Various fracture parameters studied in this experimental program are (a) Nominal strength N (b) Fracture energy, Gf (c)Fracture toughness, KIc, (c) Crack mouth opening displacement, CMOD (d) Size effect on the strength of concrete. Three-point-bend (TPB) specimen was chosen for the experimental study. Six different concrete mixes viz. A-mix, B-Mix, C-mix, D-Mix, E-mix, F-Mix were used. Acoustic Emission (AE) experiments are conducted to relate acoustic emission energy to fracture energy. It is interesting to note that both acoustic emission energy and fracture energy have similar characteristics. The advantage of the above relationship is that now it is possible to evaluate fracture energy by non-destructive testing methods. The b-value analysis of AE was carried out to study the damage in concrete structures. The Guttengberg-Richter relation for frequency versus magnitude can be applied to the AE method to study the scaling of the amplitude distribution of the acoustic emission waves generated during the cracking process in the test specimen at laboratory or in engineering structures. In the next part of this chapter b-value at various stages of damage of a reinforced concrete beam are obtained experimentally under typical cyclic loadings. The b-values at different levels of damage are tabulated. As fracture is size dependent, it may not be very useful unless its size dependency is eliminated. An effort is made to obtain size independent fracture energy by a hybrid technique.

Thermal cracking of asphalt concrete pavements is responsible for millions of dollars in annual maintenance and rehabilitation costs in the United States and Canada. Thermal cracking is typically associated with low temperatures in northern climates and at high elevations. However, another form of thermal cracking, known as thermal fatigue cracking, has been proposed by several researchers as a potential mode of distress in regions with relatively moderate climates but significant differences in high and low daily temperatures. The primary purpose of the research reported herein was to evaluate the possibility of occurrence of the thermal fatigue cracking mode of distress. A secondary objective was to identify a suitable laboratory test procedure to facilitate a mechanistic analysis of the thermal fatigue mode of distress. In light of these objectives, several laboratory test procedures were evaluated in the bituminous materials laboratory at Oregon State University (OSU). The test procedures evaluated included the phenomenological Thermal Stress Restrained Specimen Test (TSRST), the Energy Rate Integral Test (ERIT), the Direct Tension Test under constant rate of extension (DTT), and the Direct Tensile Creep Test (DTCT). The TSRST results were used to evaluate the possibility of occurrence of the thermal fatigue mode of distress. The ERIT, DTT, and DTCT procedures were evaluated with respect to the identification of a suitable laboratory test procedure to facilitate a mechanistic analysis of thermal fatigue. The results from the laboratory test program indicate that thermal fatigue distress in asphalt concrete mixtures is not a viable mode of distress in the absence of environmental aging. Based on the data presented herein and the results of previous researchers, it is evident that distress often attributed to thermal fatigue cracking is more likely the result of low temperature cracking of environmentally aged mixtures, and/or subgrade-related distress; fatigue distress due to thermal loading of semi-restrained pavements does not occur. / Graduation date: 1993

The corrosion of the reinforcing steel in concrete by de-icing salts is one of the major issues concerning the durability of reinforced concrete. Different methods have been used to protect the reinforcing steel, but still corrosion of reinforced structures continues to be a big problem causing enormous costs in their restoration and rehabilitation. The continuity of the pores of concrete plays a crucial role in the corrosion of the reinforcing steel. The ingress of corrosive species, such as chloride ions, oxygen and water, through the pores of the concrete cover cause the breakdown of the passive layer formed on the steel by the high pH of the concrete. The use of supplementary cementitious materials (SCM) in the production of high performance concrete (HPC) improves its resistance to corrosive species as a result of the pozzolanic reaction which forms more calcium silicate hydrates (C-S-H). Most of the studies about the corrosion of the reinforcement in HPC have been carried out in sound concrete. However, very few works have been reported on the corrosion of steel in cracked concrete. The crack pattern on HPC is very distinct from that formed on ordinary portland cement (OPC) concrete, which may result in different corrosion mechanisms of the reinforcing steel. The objective of the present work consisted in the evaluation of the corrosion of reinforcing steel in cracked HPC and OPC concrete under different exposure and loading conditions. For that purpose, two sets of beams of HPC (containing fly ash or slag) and two sets of OPC concrete were cast. The difference between the OPC concretes was the date of casting. Three sets of reinforcing steel probes were embedded in each beam at different locations. All the beams were cracked at midspan by the four-point method. Eight beams of each concrete were coupled in pairs and partially immersed in a solution of de-icing salts every two weeks. In this way, one set of the corrosion probes was non-submerged (top) while the other two were completely submerged (one at the crack level and the other at the bottom). Two pairs of beams were subjected to static loading whereas the other two were under cyclic loading. The corrosion potentials readings were taken daily by a data acquisition system, whereas the corrosion rates were determined by the Linear Polarization technique using a corrosion monitoring system. According to the results obtained, the corrosion rates of the submerged and non-submerged probes are very low. This behaviour is observed for the four concretes and for both loading conditions. The type of loading did not influence the corrosion rates of these probes, which were in the same range for all the concretes. On the other hand, the probes close to the crack showed higher corrosion rates, especially those under cyclic loading. In general, the OPC concrete cast during the winter presented the highest corrosion rates for both loading conditions, followed by the OPC concrete cast in the summer (as were both HPCs), then by HPC-Slag and HPC-Fly Ash, which showed the lowest values. In most of the cases there was a good agreement between the corrosion potentials and the corrosion rates, so that the OPC concretes exhibited the most negative values. The lower corrosion of the probes in the HPC-Fly Ash and HPC-Slag beams was ascribed to the continued pozzolanic activity, which may result in the self-healing of the crack with time. The probes close to the crack in the dynamically loaded beams experienced higher corrosion than those in the static beams. In some cases the corrosion rate reached values above 100 mm/year. The lower corrosion of the probes in the static beams was attributed to the self-healing of the crack. The formation of additional microcracks in the dynamic beams during cyclic loading may be responsible for their higher corrosion. The corrosion potential of the rebar cage shifted to more negative values during cyclic and static loading. This change in the potential was associated with stress concentration of the reinforcement surface, making it more active. Although the shift in the potential was not really significant, this may have important consequences in practice where the concrete is subjected to higher loads.

The corrosion of the reinforcing steel in concrete by de-icing salts is one of the major issues concerning the durability of reinforced concrete. Different methods have been used to protect the reinforcing steel, but still corrosion of reinforced structures continues to be a big problem causing enormous costs in their restoration and rehabilitation. The continuity of the pores of concrete plays a crucial role in the corrosion of the reinforcing steel. The ingress of corrosive species, such as chloride ions, oxygen and water, through the pores of the concrete cover cause the breakdown of the passive layer formed on the steel by the high pH of the concrete. The use of supplementary cementitious materials (SCM) in the production of high performance concrete (HPC) improves its resistance to corrosive species as a result of the pozzolanic reaction which forms more calcium silicate hydrates (C-S-H). Most of the studies about the corrosion of the reinforcement in HPC have been carried out in sound concrete. However, very few works have been reported on the corrosion of steel in cracked concrete. The crack pattern on HPC is very distinct from that formed on ordinary portland cement (OPC) concrete, which may result in different corrosion mechanisms of the reinforcing steel. The objective of the present work consisted in the evaluation of the corrosion of reinforcing steel in cracked HPC and OPC concrete under different exposure and loading conditions. For that purpose, two sets of beams of HPC (containing fly ash or slag) and two sets of OPC concrete were cast. The difference between the OPC concretes was the date of casting. Three sets of reinforcing steel probes were embedded in each beam at different locations. All the beams were cracked at midspan by the four-point method. Eight beams of each concrete were coupled in pairs and partially immersed in a solution of de-icing salts every two weeks. In this way, one set of the corrosion probes was non-submerged (top) while the other two were completely submerged (one at the crack level and the other at the bottom). Two pairs of beams were subjected to static loading whereas the other two were under cyclic loading. The corrosion potentials readings were taken daily by a data acquisition system, whereas the corrosion rates were determined by the Linear Polarization technique using a corrosion monitoring system. According to the results obtained, the corrosion rates of the submerged and non-submerged probes are very low. This behaviour is observed for the four concretes and for both loading conditions. The type of loading did not influence the corrosion rates of these probes, which were in the same range for all the concretes. On the other hand, the probes close to the crack showed higher corrosion rates, especially those under cyclic loading. In general, the OPC concrete cast during the winter presented the highest corrosion rates for both loading conditions, followed by the OPC concrete cast in the summer (as were both HPCs), then by HPC-Slag and HPC-Fly Ash, which showed the lowest values. In most of the cases there was a good agreement between the corrosion potentials and the corrosion rates, so that the OPC concretes exhibited the most negative values. The lower corrosion of the probes in the HPC-Fly Ash and HPC-Slag beams was ascribed to the continued pozzolanic activity, which may result in the self-healing of the crack with time. The probes close to the crack in the dynamically loaded beams experienced higher corrosion than those in the static beams. In some cases the corrosion rate reached values above 100 mm/year. The lower corrosion of the probes in the static beams was attributed to the self-healing of the crack. The formation of additional microcracks in the dynamic beams during cyclic loading may be responsible for their higher corrosion. The corrosion potential of the rebar cage shifted to more negative values during cyclic and static loading. This change in the potential was associated with stress concentration of the reinforcement surface, making it more active. Although the shift in the potential was not really significant, this may have important consequences in practice where the concrete is subjected to higher loads.

Sustainable resource management and development have been at the forefront of important issues concerning the construction industry for the past several years. Specifically, the use of sustainable building materials and the reuse and recycling of previously used building materials is gaining acceptance and becoming common place in many areas. As one of the most commonly used building materials in the world, concrete, composed of aggregate, sand, cement and water, can be recycled and reused in a variety of applications. Using crushed concrete as fill and subgrade material under roads, sidewalks and foundations has been the most common of these applications. However, research has been ongoing over the past 50 years in many countries including Germany, Canada, Japan, the United States, China, and Australia investigating the use of crushed concrete from demolished old concrete structures to fully or partially replace the virgin aggregate used to produce new concrete for use in building and pavement applications. Producing concrete using recycled concrete aggregates (RCAs) has several advantages, namely, the burden placed on non-renewable aggregate resources may be significantly decreased, the service life and capacity of landfill and waste management facilities can be extended, and the carbon dioxide emissions and traffic congestion associated with the transport of virgin aggregates from remote sites can be reduced. This research is directed at benchmarking typical RCA sources for usage in structural concrete and investigating the inter-relationships between aggregate properties, concrete properties and the bond properties between reinforcing steel and RCA concrete. The experimental program focused on four main areas: aggregate properties testing, development of concrete mixture proportions, concrete fresh and hardened properties testing, and beam-end bond testing. Four coarse aggregate sources were investigated including one virgin or natural aggregate (NA) source, and three RCA sources. Two RCA sources were derived from the crushing of decommissioned building and pavement structures (RCA-1 and RCA-2) while the third source was derived from the crushing of returned ready-mix concrete (RCA-3). A variety of typical and non-typical aggregate tests were performed to provide a basis for correlation with fresh and hardened concrete properties results. A total of 24 concrete mixtures were developed and divided into three separate categories, 1) control, 2) direct replacement, and 3) strength-based mixtures. The control mixtures were proportioned to achieve compressive strengths of 30, 40, 50 and 60MPa with slump values between 75 and 125 mm and served as a basis for comparison with the RCA concrete mixtures. The direct replacement mixtures were developed to investigate the effect that fully replacing (i.e., 100% replacement by volume) virgin coarse aggregate with RCA has on the fresh and hardened properties of the resulting concrete. The strength-based mixtures were developed to investigate the influence of aggregate properties on reinforcement bond in concrete having the same compressive strength. In addition, two separate experimental phases were carried out which had varying compressive strength ranges, different RCA sources, and different suppliers of the same type GU cement. Concrete properties such as slump, compressive strength, splitting tensile strength, modulus of elasticity, Poisson’s ratio, linear coefficient of thermal expansion (LCTE), modulus of rupture and fracture energy were all measured. In total, 48 beam-end specimens were tested that incorporated three bonded lengths (125, 375, and 450 mm) and four concrete compressive strengths (30, 40, 50 and 60 MPa). Based on the results of the aggregate testing it was found that concrete incorporating pre-soaked (i.e., fully saturated) RCA as a 100% replacement for natural aggregate had slump values between 22% and 75%, compressive strengths between 81% and 137%, splitting tensile strengths between 78% and 109%, modulus of elasticity values between 81% and 98%, LCTE values in the same range, flexural strengths between 85% and 136%, and fracture energies between 68% and 118%, of the equivalent control (natural aggregate) concrete mixture. Overall, reductions in bond strength between natural aggregate and RCA concrete ranged between 3 and 21%. The strength of coarse aggregate as quantified by the aggregate crushing value (ACV) was found to be the most significant aggregate property for influencing bond strength. A regression model (based on the beam-end specimens test results) was developed to extrapolate the experimental development lengths as a function of f’c1/4 and ACV. The model, while not intended for use as a design equation, predicted that the required development lengths for the RCA concrete tested as part of this research study were up to 9% longer as compared to the natural aggregate concrete. A detailed flowchart of the various inter-relationships between aggregate properties, concrete properties and reinforced concrete bond properties was compiled based on the results of this research. A comprehensive guideline for use of RCA in concrete was developed based on the findings of this research. It includes a systematic decision tree approach for assessing whether a particular RCA source can be categorized into one of three performance classes. The range of allowable applications of a concrete which incorporates the RCA source as replacement of natural coarse aggregate will depend on the RCA performance class.

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