Automated Surface Wave Measurements For Evaluating The Depth Of Surface-Breaking Cracks In Concrete

The primary objective of this study is to investigate the feasibility of an innovative surface-mount sensor, made of a piezoelectric disc (PZT sensor), as a consistent source for surface wave velocity and transmission measurements in concrete structures. To this end, one concrete slab with lateral dimensions of 1500 by 1500 mm and a thickness of 200 mm was prepared in the laboratory. The concrete slab had a notch-type, surface-breaking crack at its center, with depths increasing from 0 to 100 mm at stepwise intervals of 10 mm. A PZT sensor was attached to the concrete surface and used to generate incident surface waves for surface wave measurements. Two accelerometers were used to measure the surface waves. Signals generated by the PZT sensors show a broad bandwidth with a center frequency around 40 kHz, and very good signal consistency in the frequency range from 0 to 100 kHz. Furthermore, repeatability of the surface wave velocity and transmission measurements is significantly improved compared to that obtained using manual impact sources. In addition, the PZT sensors are demonstrated to be effective for monitoring an actual surface-breaking crack in a concrete beam specimen subjected to various external loadings (compressive and flexural loading with stepwise increases). The findings in this study demonstrate that the surface mount sensor has great potential as a consistent source for surface wave velocity and transmission measurements for automated health monitoring of concrete structures

Numerical Analysis of Reflective Cracking in an Asphalt Concrete Overlay over a Flexible Pavement

Previous studies have typically illustrated the three cracking mechanisms: (1) thermally induced fatigue due to a horizontal movement, (2) traffic induced fatigue due to vertical differential movement, and (3) surface initiated cracking due to the curling/warping of underlying slabs. Although these mechanisms are commonly observable for asphalt concrete overlay over both flexible and rigid pavements, the behavior and response of asphalt concrete (AC) overlay over a flexible pavement may be somewhat different from those over a rigid pavement due to their different characteristics of material and structure. Approximately 94% of 2.27 million miles of paved roads in the United States are overlaid with asphalt concrete. The mechanism of reflective cracking in AC overlays over flexible pavements has not been separately differentiated. Moreover, the bonding condition between AC overlays and flexible pavements is commonly assumed as bonded condition, although the interface condition can vary. This paper investigates the reflective cracking mechanism in an AC overlay over flexible pavements under different loading conditions by using a finite element (FE) analysis with bonded and unbonded conditions. The FE simulations also include partial top-down cracking conditions in the underlying flexible pavement. Deformed crack shapes and the highest stress concentration under traffic loading were investigated so that the initiation and propagation of reflective cracking are clearly understood. © ASCE 2014

Leaching Behavior Of Concrete Containing Municipal Solid Waste Incineration Bottom Ash

The object of this study was to investigate the impacts of municipal solid waste incineration (MSWI) bottom ash (BA) regarding cement hydration and leaching when used cement-based materials. As a mean of cement hydration assessment, energy dispersive X-ray (EDS) and X-ray diffraction (XRD) analysis were conducted on MSWI BA \u27as is\u27, hydrated BA, and BA-combined cement paste. The results show that MSWI BA led to small amount of cement hydration. In addition, the leaching characteristics of major alkaline and trace elements from concrete containing varied amounts (10%-50%) of BA were investigated by synthetic precipitation leaching procedure (SPLP) batch testing. The results reveal that the release of highly alkaline elements increases with increasing the BA content. However, the release of selected alkaline and trace heavy metals is reduced when mixed with PCC properly due to the binding effect in cement mixtures and consuming from cement hydration. Results show that crushed PCC mixed with the MSWI BA demonstrated significant reduction of Al and Si. Moreover, Mg ranged from 475.9 μg/L for the 100% BA to 181.3 μg/L for the PCC with 50% BA and Cu ranged from 45.5 μg/L to 15.1 μg/L

Mechanical Characterization Of Asphalt Tear-Off Roofing Shingles In Hot Mix Asphalt

In the USA, asphalt tear-off roofing shingle is one of the largest productions in the municipal solid waste (MSW) stream. Applications into road construction materials can be an alternative to recycle these tear-off shingles. This paper discusses the beneficial use of tear-off shingles in Hot-Mix Asphalt (HMA) by presenting: (1) the physical properties of tear-off shingles and the extracted binder, (2) the mechanical behaviors and properties of shingle-mixed HMA, (3) an optimum mix design for the shingle used in HMAs. The tear-off shingles obtained from the states of Florida and Minnesota (but main study on the Florida\u27s shingles) were used for the sample preparation that involves varied amount of shingle addition (ranged from 0% to 6% with 1% increment) for three different virgin binder contents. Laboratory testing methods include a reflux extraction and recovery and penetration tests for the extracted binder and a modified Marshall stability, moisture susceptibility, and asphalt pavement analyzer (APA) tests for the mixtures. The shingle addition causes stiffer binder in the mixture, resulting in the increase of material stiffness, stability, and rutting resistance. A visual inspection of the fractured surface of samples was also conducted to investigate the location of the crack surface either through the aggregates or in the asphalt binder, which is a good indicator of sufficient level of asphalt film in the mixture. Testing results were used to identify the optimum mixing proportion of the tear-off shingle and asphalt binder in HMAs. © 2013 Published by Elsevier Ltd

Bearing Capacity and Mechanism of the H–V Geogrid-Reinforced Foundation

A series of model tests were conducted to investigate the bearing capacity and reinforced mechanism of a horizontal–vertical (H–V) geogrid-reinforced foundation. The bearing capacities of the unreinforced foundation, the conventional geogrid, and the H–V geogrid-reinforced foundation were compared. The parameters, including the length of the H–V geogrid, the vertical geogrid height, the depth of the top layer, and the number of H–V geogrid layers, are discussed. Through experiments, it was found that the optimal length of H–V geogrid is around 4B, the optimal vertical geogrid height is approximately 0.6B, and the optimal depth of the top H–V geogrid layer is between 0.33B and 1B. The optimal number of H–V geogrid layers is 2. The result also indicates that the bearing capacity of H–V geogrid is almost 1.7 times greater than that of conventional geogrid. Additionally, the maximum top subsidence of H–V geogrid-reinforced foundation decreased by 13.63% compared to that of conventional geogrid-reinforced foundation. Under the same settlement, the bearing capacity ratio of two H–V geogrid-reinforced foundation layers is 75.28% higher than that of one layer. The results also demonstrate that the vertical elements of H–V geogrid interlock the sand from being displaced under the applied load and redistribute the surcharge over a wider area, thereby increasing the shear strength and improving the bearing capacity of an H–V geogrid-reinforced foundation

Evaluation Of Recementation Reactivity Of Recycled Concrete Aggregate Fines

The use of recycled concrete aggregate (RCA) as a drainage material in exfiltration trenches and base and subbase layers is becoming increasingly common. During crushing, stockpiling, transporting, and placing, however, RCA may produce fines that could recement and clog the pavement drainage system. Many previous studies indicated that not only the structural capacity but also drainage of pavement subsurface layers can be greatly affected by the properties and gradation of the aggregate used. This study evaluated the recementation reactivity of RCA fines that could eventually impair drainage performance. RCA fines passing the No. 200 sieve (less than 75 μm) were produced through the simulation of an in-place aggregate abrasion process, and cement paste cylinders were cast with complete replacement of cement with RCA fines. The hydration properties of the paste samples with RCA fines were evaluated by means of heat of hydration, pH variation, and Vicat needle penetration in their early age. Compressive strength tests and petrographic examinations such as scanning electron microscopy, energy dispersive X-ray, and X-ray diffraction were also performed to mechanically and chemically verify the recementation reactivity of the hardened paste with RCA fines. Test results demonstrated that recementation of RCA fines was modest, and therefore the compressive strength of the paste specimens with RCA fines was minimal compared with that of ordinary cement paste specimens. The microstructural and chemical composition analyses also indicated that the recementation reactivity of RCA fines was negligible

Understanding Florida\u27S Sinkhole Hazards: Hydrogeological Laboratory Study

Sinkholes pose a hazard socially, economically and environmentally. In Florida, sinkhole-related insurance claims between 2006 and 2010 amounted to $1.4 billion. The scope of this study is to develop a sinkhole simulator (soil-groundwater physical testing) that can assess the qualitative behavior of the hydrogeological mechanism of sinkhole formation. The physical model setup incorporates an unconfined and confined aquifer system with constant head controls for each. Water level transducers are used to monitor variations in the water table during the sinkhole process. The study investigates effects of sinkhole affecting parameters such as soil type and compaction level. Scenarios involving adjustments in soil type and compaction are employed to collect data on water table drawdown and erosion characteristics, as well as the type of sinkhole formation, either cover-collapse or cover-subsidence. A strong relationship between soil compaction, cohesion and the type of sinkhole formed was observed

Drainage Performance Evaluation of Reclaimed Concrete Aggregate

Reclaimed concrete aggregate (RCA) is used as replacement or mixed with virgin aggregates to be used in embankments, hot-mix asphalt (HMA), Portland cement concrete, and base/sub-base layers in pavement systems. However, RCA has not received a lot of attention as a drainage media because of low abrasion resistance, which causes excess fines content, and the potential of clogging material on filter fabrics. The performance of RCA as drainage material has not been evaluated by many researchers, and the limited information restricts its use. This paper describes the testing methods used to evaluate RCA as a French drain material; the French drain system collects water runoff from the road pavement and transfers it to slotted pipes underground and then filters through aggregate. RCA was tested for its physical properties including specific gravity, unit weight, percent voids, absorption, and abrasion resistance. RCA cleaning/washing methods were also applied to evaluate the fines removal processes. A petrographic examination was conducted by using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray diffracation (XRD). The permeability of RCA was also tested using the No. 4 gradation. The results showed that RCA has a high abrasion value, that is, it is very susceptible to breaking down from abrasion during transportation, stockpiling, or placing. The permeability tests show that the No. 4 gradation does not restrict the flow of water; however, the flow rate is highly dependent on the hydraulic system itself. © ASCE 2014

Clogging Potential of Recycled Concrete in Road Drainage

Recycled concrete aggregate (RCA) is often used as a replacement or partial replacement of virgin aggregate. Commonly RCA is used in road foundations (base course), embankments, hot-mix asphalt, or Portland cement concrete. However the use of RCA in drainage systems, such as French drains, is currently prohibited in the state for Florida. The primary concerns with using RCA as a drainage media are the fines content and the precipitation of calcium carbonate to cause a reducing in filter fabric permittivity. Not much research has been conducted as it relates to using RCA as a drainage material; this limited information inhibits its use in French drains. This paper describes the investigation of permeability of RCA as a No. 4 aggregate gradation and base course gradation. The effect of excess fines (passing the No. 200 sieve) and the precipitation potential of calcium carbonate have also been studied

Improvement Of Crack-Detection Accuracy Using A Novel Crack Defragmentation Technique In Image-Based Road Assessment

A common problem of crack-extraction algorithms is that extracted crack image components are usually fragmented in their crack paths. A novel crack-defragmentation technique, MorphLink-C, is proposed to connect crack fragments for road pavement. It consists of two subprocesses, including fragment grouping using the dilation transform and fragment connection using the thinning transform. The proposed fragment connection technique is self-adaptive for different crack types, without involving time-consuming computations of crack orientation, length, and intensity. The proposed MorphLink-C is evaluated using realistic flexible pavement images collected by the Florida Department of Transportation (FDOT). Statistical hypothesis tests are conducted to analyze false positive and negative errors in crack/no-crack classification using an artificial neural network (ANN) classifier associated with feature subset selection methods. The results show that MorphLink-C improves crack-detection accuracy and reduces classifier training time for all 63 combinations of crack feature subsets that were tested. The proposed method provides an effective way of computing averaged crack width that is an important measure in road rating applications