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Internal vibration is a commonly used method for consolidating fresh concrete. Proper vibration causes entrapped air voids to float to the surface of the concrete or collapse at the water–air interface. However, if vibration is excessive, it may introduce air into the concrete under certain circumstances. The consequence of this is an uneven distribution of air voids, resulting in heterogeneous concrete and subsequently undesirable strength and freeze–thaw durability. This study investigated the mechanism by which air voids are induced in concrete due to vibration. Concrete mixtures were prepared and vibrated at several frequencies for a range of durations. Air-void distribution within different zones from each sample was obtained using the linear traverse method. It was found that rotary movement of a high-frequency, vertical vibrator created a vortex inside the liquefied fresh concrete that sucked air into the concrete from the surface. In general, increasing the frequency of vibration will cause more air addition, and the amount of air added with increasing duration of vibration is dependent on the amount of unreacted air-entraining agent (AEA) remaining in the system. [ABSTRACT FROM AUTHOR]

Electrically-conductive concrete (ECON) can generate heat for melting pavement ice if an electrical voltage is applied, and this ECON-heated pavement system (HPS) is a viable alternative to the traditional snow removal methods. This study aimed at determining mixture proportions and procedures suitable for ready-mix concrete-plant-produced carbon fibre (CF)-reinforced ECON. Trial batches ECON production involving five different mixture proportions and procedures were performed at a ready-mix concrete plant. Study results suggest that CF begins to degrade with increased mixing time. A twelve-minute mixing time from the start of loading CF onto the mixer until the end produced the best-performing ECON, with an electrical resistivity of 224 Ω-cm and a heat-generation rate of 2°C/min. Scanning electron microscopic (SEM) image analysis shows that CF remained as blobs of fibre instead of being uniformly dispersed. Further research is recommended to find an efficient way of separating individual CF from the blobs and ensuring uniform CF dispersion to reduce the dosage rate and construction cost of ECON. [ABSTRACT FROM AUTHOR]

Air voids in concrete tend to cluster around coarse aggregate particles and potentially weaken the concrete. This study explored key factors influencing air void clustering and evaluated the effect of air void clustering on concrete strength. The six considered variables were cement type (low alkali cement and limestone cement), fly ash (with the low and high loss on ignition), coarse aggregate type (limestone and gravel), admixture combination type (stable and unstable air-entraining agents and compatible and incompatible water reducers), mixing temperature (70 and 90°F), and workability (with and without retempering). A total of 64 mixtures were prepared and tested. The fresh concrete's slump, unit weight and air content were studied along with its compressive strength after 7 and 28 days. Air-void spacing factor, clustering and the voids' specific surface were evaluated. The results showed that retempering was the most significant factor influencing air void clustering. It was found that retempering can increase air content, create finer air voids and aggravate air void clustering. To reduce the risk of air void clustering, retempering and the mixing water temperature of 90°F should be avoided. When the clustering rating exceeded 0.6, some strength loss was observed. [ABSTRACT FROM AUTHOR]

In recent years, the implementation of a sustainable concrete system has been a great topic of interest in the field of construction engineering worldwide as a result of the large and rapid increase in carbon emissions and environmental problems from traditional concrete production and industry. The compressive and tensile strength of the TSC that had RCA was improved by the addition of bagasse ash. Incorporating GSP refines the pore structure to the greatest extent and improves the compressive strength and chloride ion penetrability resistance of high-strength concrete. Compared with rectangular and V-shaped cracks, the chloride diffusion process in cracked concrete with a tortuous crack was slower at the early immersion age, while the crack geometry had a marginal influence on the chloride penetration depth in cracked concrete during long-term immersion. [Extracted from the article]

The use of concrete overlays has long been recognised as a cost-effective pavement maintenance and rehabilitation strategy. However, the long-term performance of various types of concrete overlays has not been fully investigated since there has not been enough performance data available to conduct such an evaluation. Concrete overlays have been regularly constructed on Iowa roadways since the late 1970s and many older projects are still in use. Performance-related data for in-service concrete overlays have been acquired from the available resources to evaluate long-term performance of concrete overlays in Iowa. The information collected includes Pavement Condition Index (PCI), International Roughness Index (IRI), overlay type, construction year, overlay thickness, joint spacing, traffic, and other construction and design-related data. Based on an evaluation of PCI and IRI changes during service life, it is observed that concrete overlays can provide at least 20 years of service life. In terms of PCI ratings, 89% of concrete overlays investigated have PCI values greater than 60% as of the time of the analysis. Similarly, 93% of concrete overlays have IRI values lower than 2.7 m/km (170 in/mile). The effects of overlays type and design features on long-term performance of Iowa concrete overlays are also discussed. [ABSTRACT FROM AUTHOR]

Although internal vibration has been widely implemented in concrete pavements, reports about concrete deterioration caused by improper vibration have been emerging. This study investigates the transmission of vibration energy, water movement, and air movement in concrete under vibration to provide the experimental basis for a better understanding of vibration in different concrete mixtures. An innovative experimental method was developed to measure energy transmission in concrete. The mixtures varied by air content, slump, and water-reducing admixture addition and were prepared to test the vibration energy, water absorption, and the air-void system for a range of vibrator frequencies. The vibration energy transferred through the mixture generally displayed a linear rise, then a slight drop, and, finally, stability, indicated by both measurements of transferred energy and voltage demand of the vibrator. The magnitude of vibration energy transferred through the mixtures increased with an increasing slump. For all samples tested, water appeared to move away from the vibrator, most markedly with an increasing frequency. There is a clear indication of air movement to the surface of the concrete in all tested samples. [ABSTRACT FROM AUTHOR]

In this study, the mechanical properties of concrete mixtures containing different cementitious combinations and two aggregate systems were investigated under plastic and drying conditions. Emphasis was laid on the durability and shrinkage of concrete. Life cycle analysis (LCA) was also conducted by using the Green Concrete LCA web tool. Results indicated that the presence of larger aggregate sizes tend to enhance durability of concrete. The presence of nanosilica also imparted superior mechanical properties to concrete. A cementitious combination containing Portland limestone cement and fly ash with larger aggregate sizes emerged as a better performing mixture in terms of mechanical properties and with minimum environmental impact. [ABSTRACT FROM AUTHOR]

In this work, different cementitious systems were used to investigate the shrinkage of concrete under plastic and drying conditions. Emphasis was placed on Portland limestone cement (type IL) with replacement amounts of 10% of Portland cement. Comparisons were made with a cement type with low Blaine fineness (i.e. coarse ground cement). The results indicated that type IL cement has good shrinkage results without adversely affecting other engineering properties of concrete such as strength, resistivity, degree of hydration and setting time. This is probably due to improved particle packing, access to more nucleation sites for the hydration products and the formation of calcium carbo-aluminate hydrates. Scanning electron micrographs of coarse ground cement paste also indicate a retarded degree of hydration compared to type I/II Portland cement paste. [ABSTRACT FROM AUTHOR]

The science of rheology is not strictly applicable for low workability of slipform concrete mixtures because such mixtures are not fluids. However, the workability of slipform concrete mixtures can be assessed using the concepts behind describing rheological behaviour. Understanding the workability of a mixture is important for construction activities to achieve a successful pavement. Too dry a mixture may cause problems achieving sufficient consolidation, while too wet a mixture may result in edge slump. The novel workability test method (vibrating Kelly ball test or VKelly test) presented in this paper quantitatively assesses the responsiveness of a dry concrete mixture to vibration, as desired of a slipform paving mixture. The development process was carried out in three phases to achieve cost-effectiveness, portability, ability to assess critical performance parameters and repeatability. The three phases were assessing the sensitivity of the VKelly test to check whether it can signal variations between laboratory mixtures with a range of materials and proportions, evaluating the test in field applications at a number of construction sites and validating the test against the box test developed at Oklahoma State University. The VKelly test appears to be suitable for assessing a mixture's response to vibration (workability) with a low multiple operator variability. A unique parameter, the VKelly index, is introduced, and a mixture in the range of 2·0-3·0 cm/s1/2 seems to be suitable for slipform paving. [ABSTRACT FROM AUTHOR]

The purpose of this study is to investigate the effects of water-to-binder ratio (w/b), air content, and type of cementitious material on the fresh and hardened properties of binary and ternary blended concrete mixtures in pavements. This experimental program prepared a total matrix of 54 mixtures with w/b of 0.40 and 0.45; nominal air content of 2, 4, and 8%; and three types of supplementary cementitious materials and one ordinary portland cement in different combinations. Binder systems included ordinary portland cement, binary mixtures with slag cement, Classes F and C fly ash, and ternary mixtures containing a combination of slag cement and one type of fly ash. Workability, total air content, air void system parameters (i.e., spacing factor and specific surface) in fresh concrete, setting time, compressive strength, surface resistivity, and shrinkage were determined. Test results showed that ternary mixtures followed the trends of their constituent materials. Binary and ternary mixtures containing Class C fly ash and slag cement exhibited higher compressive strength than the control mixture. The surface resistivity and shrinkage results of binary and ternary mixtures were equal to or improved over the control mixture. [ABSTRACT FROM AUTHOR]

The purpose of this study is to investigate the minimum paste volume required with an appropriate water-to-cementitious ratio () to achieve required workability, strength, and durability requirements of concrete mixtures for pavements. In this experimental program, 64 concrete mixtures with varying , cementitious content, and binder type were prepared and tested. The fine aggregate-to-total aggregate ratio was held constant for all the mixtures. Fresh and hardened concrete properties of the mixtures were determined at various ages. Test results have shown that approximately 1.5 times more paste by volume is required than voids between the aggregates to achieve a minimum performance in concrete for pavements. For a given , strength is independent of cementitious content after a critical value is provided. When is constant, increasing paste content increased chloride penetrability and air permeability. [ABSTRACT FROM AUTHOR]

The purpose of this study is to investigate the minimum paste volume required with an appropriate water-to-cementitious ratio () to achieve required workability, strength, and durability requirements of concrete mixtures for pavements. In this experimental program, 64 concrete mixtures with varying , cementitious content, and binder type were prepared and tested. The fine aggregate-to-total aggregate ratio was held constant for all the mixtures. Fresh and hardened concrete properties of the mixtures were determined at various ages. Test results have shown that approximately 1.5 times more paste by volume is required than voids between the aggregates to achieve a minimum performance in concrete for pavements. For a given , strength is independent of cementitious content after a critical value is provided. When is constant, increasing paste content increased chloride penetrability and air permeability. [ABSTRACT FROM AUTHOR]

The present research aims at evaluating the mechanical performance of untreated and treated crumb rubber concrete (CRC). The study was also conducted to reduce the loss in mechanical properties of CRC. In this study, sand was replaced with crumb rubber (CR) with 0%, 5%, 10%, 15%, and 20% by volume. CR was treated with NaOH, lime, and common detergent for 24 h. Furthermore, water treatment was also carried out. All these treatments were done to enhance the mechanical properties of concrete that are affected by adding CR. The properties that were evaluated are compressive strength, indirect tensile strength, unit weight, ultrasonic pulse velocity, and water absorption. Compressive strength was assessed after 7 and 28 days of curing. The mechanical properties were decreased by increasing the percentage of the CR. The properties were improved after the treatment of CR. Lime treatment was found to be the best treatment of all four treatments followed by NaOH treatment and water treatment. Detergent treatment was found to be the worse treatment of all four methods of treatment. Despite increasing the strength it contributed to strength loss. [ABSTRACT FROM AUTHOR]

Highlights • Curing regime is a vital factor affecting concrete hardened performance. • Correlation between air-void system and salt-scaling resistance is negligible. • Salt scaling is mainly affected by sorptivity and surface hardness of the concrete. • Lower resistance of a slag concrete to salt scaling is not a physical issue. Abstract This paper is focused on evaluating the impact of curing on concrete performance, and correlating hardened performance to salt-scaling resistance of concrete. The performance of the mixtures was determined through air-void system, sorptivity, and abrasion tests. A total of seven different curing regimes were applied to mixtures made with different binary systems containing 0%, 20%, 40%, and 60% slag cement. The results obtained showed that curing affects salt-scaling potential by changing sorptivity and abrasion resistance of the mixtures. While slag-cement replacement reduced the scaling resistance of the mixtures, a replacement of up to 40% improved the mechanical and transport properties. In addition, no correlation was observed between salt scaling and the air-void system. [ABSTRACT FROM AUTHOR]

The development of novel “smart” structures by embedding sensing capabilities directly into the construction material during the manufacturing and deployment process has attracted significant attention in autonomous structural health monitoring (SHM). Micro-electromechanical systems (MEMS) provide vast improvements over existing sensing methods in the context of SHM of highway infrastructure systems, including improved system reliability, improved longevity and enhanced system performance, improved safety against natural hazards and vibrations, and a reduction in life cycle cost in both operating and maintaining the infrastructure. Advancements in MEMS technology and wireless sensor networks provide opportunities for long-term, continuous, real-time structural health monitoring of pavements and bridges at low cost within the context of sustainable infrastructure systems. Based on a comprehensive review of literature and vendor survey, the latest information available on off-the-shelf MEMS devices, as well as research prototypes, for bridge, pavement, and traffic applications are synthesized in this paper. In addition, the paper discusses the results of a laboratory study as well as a small-scale field study on the use of a wireless concrete monitoring system based on radio-frequency identification (RFID) technology and off-the-shelf MEMS-based temperature and humidity sensors. [ABSTRACT FROM AUTHOR]

Snow and ice accumulation on pavements pose formidable challenges for transportation agencies in cold regions, resulting in diminished traffic speed, traffic flow, and heightened accident risk during winter. While electrically-conductive concrete (ECON) heated pavement systems (HPS) have emerged as an ecologically-sound and cost-effective snow and ice-removal solution, a lack of identification of critical design parameters for ECON HPS impedes the development of precise design criteria for this technology. This research endeavors to comprehensively elucidate the heating process of electrically-conductive concrete (ECON) slabs and to scrutinize how the depth of electrode placement influences thermal performance. The investigation reveals that the electrode-concrete interface zone serves as the predominant heat source for ECON HPS, and if shallower electrode placement depths are used, the surface temperature increase rate of ECON slabs is enhanced, optimizing cost-effective operation. The study also establishes a threshold voltage level for ECON slabs, beyond which significant changes in electrical properties yield relatively ineffective temperature increase rates. The study found 16 VAC and 425 W/m² to be threshold values for the specific ECON slab system studied. These compelling findings offer valuable insights for future ECON slab design and implementation, ensuring efficient and practical snow-removal applications and benefiting transportation agencies and the broader community. • Identified primary heat source in ECON slabs. • Discovered threshold voltage for ECON slabs. • Explored electrode-ECON interface impact on the threshold voltage. • Investigated threshold voltage's effect on repetitive performance. • Examined electrode depth's influence on ECON slab's thermal performance. [ABSTRACT FROM AUTHOR]

Repeated deflection behavior resulting from temperature and moisture variations across concrete pavement depth causes curling and warping of Portland cement concrete (PCC) pavement systems. Although curling and warping issues have been investigated extensively, there are no standardized methods or procedures currently available to characterize the degree/magnitude of this in situ environmental load-related deflection. This study discusses the development of a detailed procedure for assessing environmental load-related deflection of concrete pavement using a Light Detection and Ranging (LiDAR) system. LiDAR systems have been recognized as an advanced technology for transportation infrastructure inspection but have not been widely investigated for measuring environmental load-related deflection of concrete pavements. In this study, field surveys were conducted on six identified concrete pavement sites in Iowa by scanning the concrete slab surfaces using the stationary LiDAR instrument. Based on dense point cloud data obtained by the LiDAR instrument, a data processing algorithm was developed to obtain the degrees of environmental load-related deflection. The degrees of deflection obtained were correlated to variations in pavement performance, mix design, pavement design, and construction details at each site. The results and findings from this study describe a potentially novel method of using LiDAR system for environmental load-related deflection characterization of concrete pavement. [ABSTRACT FROM AUTHOR]

This research was inspired by the need to optimize the mix design of electrically conductive concrete (ECON) for field implementation. Carbon fiber was used for producing ECON with different mixing proportions and constituents. Calcium nitrite-based corrosion inhibitor admixture and methylcellulose were used as conductivity-enhancing agent (CEA) and fiber-dispersive agent (FDA) respectively. Five easy-to-change mix design variables were evaluated for their effects on electrical conductivity and strength of ECON: carbon fiber dosage, fiber length, coarse-to-fine aggregate volume ratio (C/F), CEA dosage, and FDA dosage. The results approved the effectiveness of the applied CEA in improving electrical conductivity while positively influencing strength. Conductivity was significantly influenced by: fiber content, C/F, fiber length, and CEA dosage. The dosages of Fiber, CEA, and FDA exerted significant influence on compressive strength. C/F and FDA dosage were significant variables influencing flexural strength. [ABSTRACT FROM AUTHOR]

The objective of this study was to synthesize, characterize and evaluate the nanomaterials-based superhydrophobic (super water-repellent) coatings on Portland cement concrete (PCC) surfaces. These coatings are synthesized with nanomaterials such as polytetrafluoroethylene (PTFE), polyether ether ketone (PEEK) and silanized diatomaceous earth (DE). Using layer-by-layer (LBL) deposition technique, each coating type was deposited at four different spray durations. The water-repellency of the coated surfaces were characterized by measuring static water contact angles (WCAs). These measurements were evaluated through a statistical design-based experimental test program which revealed that the spray duration and coating type are significant variables. A skid-resistant coating composed of PTFE and PEEK was utilized to evaluate the impact of superhydrophobic coatings on pavement skid resistance. [ABSTRACT FROM AUTHOR]

• Characterization of paste samples by using X-Ray Micro Computed Tomography (µ-CT) and Fluorescence Microscopy techniques. • Potential relationships between paste microstructure and durability and other mechanical properties of concrete. • 3D printed hour glass shaped molds to cast paste samples. • In-house method of sample preparation. • Micro-crack density and void system in paste related to concrete shrinkage, durability and degree of hydration. In this study, paste samples from different cementitious systems were characterized by using X-Ray Micro Computed Tomography (µ-CT) and Fluorescence Microscopy techniques. Quantitative and qualitative aspects of defects from paste samples were investigated to develop indicators of durability related properties of corresponding concrete samples. In the first phase of this study, hour glass shaped 3D printed molds were used to investigate five cementitious combinations consisting of three cement types (Coarse Ground portland cement, Type IL Portland Limestone Cement and Type I/II ordinary portland cement) and fly ash as a supplementary cementitious material. In the second phase, metal molds were used to compare the results of Coarse Ground portland cement with Type I ordinary portland cement, 5% of which was replaced with colloidal nanosilica. Potential correlations between paste and concrete have been presented. This work was supported by US Department of Energy and North Dakota Department of Commerce. [ABSTRACT FROM AUTHOR]