Field Validation for the Constructability of Exposed Aggregate Concrete Overlay

Functional performance of existing concrete pavement is necessarily improved to maintain the low tire-pavement noise and the long-term skid resistance. Thus, exposed aggregate concrete overlay is introduced since these high functional performances are expected. Its surface texture requires the removal of cement mortar to expose the aggregates. This technique results a durable surface texture and an effective surface drainage through the random shape of aggregates. In Korea, concrete overlay is allowed to construct between 200 and 400 meters per day. This concrete amount is insufficient to use batch plant. Therefore, mobile mixer is employed to supply a consistent quality and on-time production. In addition, surface texture of this overlay method is significantly related to the reduction of tire-pavement noise. Accordingly, outcome of surface texture should be validated in the real field construction. This study intended to verify the constructability of exposed aggregate concrete overlay using mobile mixer for concrete production and deck finisher for concrete placement to acquire the surface texture and structural strengths. Surface texture and concrete strengths from mock-up and laboratory tests were measured and compared with design criteria. This research indicated that the suggested equipment and construction procedure can efficiently maintain the required surface texture of EACO for low tire-pavement noise and the adequate strengths for early traffic opening.

Application of the maturity method in slipforming operations

The main objective of this thesis is to study the application of the maturity method in slipforming operations so as to provide more efficient means of the construction planning of a project. The main target of this research is to use the maturity method to establish the initial setting times and then apply those times to estimate the slipform mockup time and speed. In this research various maturity functions are compared and the most efficient one is used. The apparent activation energy (E) and the temperature sensitivity factor (B) are, examined so as to understand their effect on the maturity function and also to establish a relationship between them and the retarder dosage. Furthermore, the "FHP Strength Model (SFHP)" and the "Rate Constant Model (SkY' are used to evaluate their competence in representing the strength development of a concrete mixture in the laboratory and in the field. Also, the maturity method is used to estimate the times of mockup and then compared with the "Penetration Resistance", "2°C Temperature Increase", "Rod", and "Conductivity" methods. Furthermore, an example is presented and the mock-up times are established based on various initial concrete temperatures and slipform layer arrangements. Finally a computer program is developed to establish the mockup times, time of concrete placement, and the slipform speed during the removal process. The results of this research showed that the Carino and Tank maturity function is preferred for the calculation of the maturity indexes. Also, it is found that a linear relationship between the retarder dosage and E or B can be established. Moreover, it is shown that E or B can be estimated by the method suggested by Pinto and Hover. In addition, a new strength-maturity model is suggested. Finally, it is found that the maturity method can be used with efficiency to establish the slipform mockup times, the time of the concrete layer, and the slipform speed.

Application of the maturity method in slipforming operations

The main objective of this thesis is to study the application of the maturity method in slipforming operations so as to provide more efficient means of the construction planning of a project. The main target of this research is to use the maturity method to establish the initial setting times and then apply those times to estimate the slipform mockup time and speed. In this research various maturity functions are compared and the most efficient one is used. The apparent activation energy (E) and the temperature sensitivity factor (B) are, examined so as to understand their effect on the maturity function and also to establish a relationship between them and the retarder dosage. Furthermore, the "FHP Strength Model (SFHP)" and the "Rate Constant Model (SkY' are used to evaluate their competence in representing the strength development of a concrete mixture in the laboratory and in the field. Also, the maturity method is used to estimate the times of mockup and then compared with the "Penetration Resistance", "2°C Temperature Increase", "Rod", and "Conductivity" methods. Furthermore, an example is presented and the mock-up times are established based on various initial concrete temperatures and slipform layer arrangements. Finally a computer program is developed to establish the mockup times, time of concrete placement, and the slipform speed during the removal process. The results of this research showed that the Carino and Tank maturity function is preferred for the calculation of the maturity indexes. Also, it is found that a linear relationship between the retarder dosage and E or B can be established. Moreover, it is shown that E or B can be estimated by the method suggested by Pinto and Hover. In addition, a new strength-maturity model is suggested. Finally, it is found that the maturity method can be used with efficiency to establish the slipform mockup times, the time of the concrete layer, and the slipform speed.

Modeling temperature profile in mass concrete at early ages of cement hydration

Thermally induced cracks due to temperature gradient in mass concrete have adverse effects on its durability and service life. Heat released during the hydration of Portland cement in early age mass concrete can be quite excessive depending on the ambient temperature, cement content of the concrete mix and the size. Finite difference model using Crank Nicholson implicit method was developed based on the two dimensional unsteady state heat conduction. Optimized MATLAB based software was developed for simulation and data visualization. A mass concrete block cast with standard mix ratio and water cement ratio was used to verify the efficacy of the model. Type-K thermocouple and digital thermometer were used to monitor the temperature at time intervals. The temperature profile showed a hotter core and cooler surface except for the initial placement temperature, which exhibited a uniform temperature for all thermocouple locations. Peak temperature values were recorded within the first day of concrete placement. The model successfully predicted the temperature profile of the mass concrete at early ages of cement hydration. With the knowledge of the ambient temperature and the configuration of the mass concrete, the model can reliably predict the temperature profile from which potential for thermal cracks occurrence can be determined to enable suitable proactive preventive and control measures.

FIBER CONCRETE FOR 3-D ADDITIVE TECHNOLOGIES

fine-grained fiber concrete used in 3D printing is significantly different from conventional heavy concrete, which is determined by the increased consumption of cement, low water-cement ratio and the absence of large aggregates. The largest grain size of fine aggregate is selected taking into account the thickness of the section, the frequency and type of reinforcement, as well as the method of concrete placement. Despite the fact that the tensile strength of concrete on fine sand is more than 1.5 times higher than the strength of concrete on coarse sand, while there is a decrease in compressive strength. Due to the peculiarities of the technology of concrete manufacturing for layering, the use of coarse sands is impractical, and therefore it was decided to use quartz sand with a particle size module of 1.12 as a filler.

Flexural Behavior of SCC with Copper Slag as Partial Replacement of Fine Aggregate

Natural fine aggregates are becoming more limited, and their production and consignment are turning out hard day by day. Therefore, the production of concrete needs to turn into eco-friendly construction practice. Self-Compacting Concrete (SCC) self-consolidates itself without any external vibration, and subsequently it quickens the concrete placement process and decreases the labor demands. In this study, the Flexural behavior of the SCC was studied. Reinforced SCC beam specimens were cast and tested in laboratories. The flexural behavior of SCC with copper slag as replacement for sand is delimited with the flexural test on beam specimens by examining the factors like deflection, flexural strength, crack pattern and strain pattern.

Analytical model for prediction of temperature distribution in early age mass concrete

Thermally induced cracks have far-reaching implications on the durability of concrete structures. When cement mixes with water, the reaction is exothermic implying the release of heat. In the case of mass concrete structures, quite a substantial increase in internal temperature may be experienced depending on the ambient temperature and cement content in the mix. The objective of the paper is to develop a mathematical model to predict the time dependent temperature profile in early age mass concrete. Mass concrete block was used to verify the model. Type-K thermocouples placed at various positions and digital thermometer was used to monitor the temperature distribution within the mass concrete block at intervals. The highest temperature values occurred within the core of the mass concrete after one day of concrete placement. Analytical model was developed by applying method of separation of variables and orthogonality relation to two dimensional unsteady state heat conduction equations. The model equation was evaluated and using MATLAB based computer programe. The model successfully predicted the temperature variation within the mass concrete with time. It is therefore suitable for use in the assessment of thermal cracks potential in mass concrete structures.

Fiber Concrete for 3-D Additive Technologies

Fine-grained fiber concrete used in 3D printing is significantly different from conventional heavy concrete, which is determined by the increased consumption of cement, low water-cement ratio and the absence of large aggregates. The largest grain size of fine aggregate is selected taking into account the thickness of the section, the frequency and type of reinforcement, as well as the method of concrete placement. Despite the fact that the tensile strength of concrete on fine sand is more than 1.5 times higher than the strength of concrete on coarse sand, while there is a decrease in compressive strength. Due to the peculiarities of the technology of concrete manufacturing for layering, the use of coarse sands is impractical, and therefore it was decided to use quartz sand with a particle size module of 1.12 as a filler.

A Review on Pull out Test on Exterior Beam-Column joint

Conventional concrete loses its tensile resistance after the formation of multiple cracks. However, fibrous concrete can sustain a portion of its resistance following cracking to resist more loading. Use of the headed bar can offer a potential solution for these problems and may also ease fabrication, construction, and concrete placement. There have been many catastrophic failures reported in the past earthquakes, with Turkey and Taiwan earthquakes occurred in 1999, which have been attributed to beam–column joint failures. To achieve this performance level, special steel reinforcement details are required in the beam–column joint region of reinforced concrete framed structures. The experimental work carried out on four different arrangements of reinforcement of beam column joints. The aim of the research is to investigate the pull-out behavior such as strength, failure mode, and crack patterns of different arrangements of reinforcement in exterior beam column junctions. The transverse reinforcement of a joint reduces stresses by improving the confinement of concrete. All joints were tested by using reversed cyclic loading. In the first arrangement, the beam bars are extended in the column for distance Ld + (10xDia) from the inner face of column. This research studies the experimental behavior of full-scale beam-column space (three-dimensional) joints under displacement-controlled cyclic loading. Eleven joint specimens, included a traditionally reinforced one (without adequate shear reinforcement), a reference one with sufficient shear reinforcement according to ACI 318, and nine specimens retrofitted by ferrocement layers, were experimentally tested to evaluate a retrofit technique for strengthening shear deficient beam column joints.

Using seismoacoustic sounding technique for the purpose of structural integrity evaluation of the solid reinforced-concrete foundation for the power transmission line supports

During construction of the monolithic reinforced-concrete foundation, it is not easy to monitor both a continuous haulage and technology of concrete placement. For that matter, some breach of the foundation structural integrity may occur. Currently, there is no unanimous integrated practice of monitoring concrete placement for building oversize solid reinforced-concrete foundations. The surveying results of the solid concrete foundation dimensioned 16m by 16m and from 2 to 3.5m thick are set forth in the article. Such geophysical technique as seismoacoustic sounding has proved effective for concrete placement quality control of monolithic reinforced-concrete foundations by means of a non-destructive method.