BooHyun Nam

Leaching behaviour of municipal solid waste incineration bottom ash mixed with Hot-Mix Asphalt and Portland cement concrete used as road construction materials

One of the beneficial utilisations of municipal solid waste incineration (MSWI) bottom ash (BA) is in the area of road construction sector: for example, the partial replacement of fresh aggregate in Hot-Mix Asphalt (HMA) and Portland cement concrete (PCC). However, the potential leaching of toxic elements (e.g. alkaline elements and heavy metals) from the BA mixed with milled HMA and crushed PCC is still a concern when used as 2nd-cycle recycled materials. This paper presents and discusses the chemical characteristics and leaching behaviour of MSWI BA when used in both HMA and PCC. Chemical analysis of MSWI BA was conducted by using petrographic analysis tools. The leaching characteristics of major alkaline and trace elements from the milled HMA and crushed PCC containing varied amounts of BA were investigated by Synthetic Precipitation Leaching Procedure (SPLP) batch testing. The release of most alkaline and heavy metals (except Mg and Si from HMA and Ca from PCC) is reduced when mixed with the HMA and PCC as adding 10–20% of BA due to the binding effect in asphalt and cement mixtures. The concentrations of most major alkaline elements (e.g. Ca, Al, Si, and Na) from the HMA and PCC with BA increased with increasing elapsed time due to availability controlled leaching. The release of all of the priority elements meets the criteria of the US Secondary Drinking Water Standard (except Al) and the EPA Multi-Sector General Permit for Stormwater Discharges Associated with Industrial Activity.

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.

An optimum selection strategy of reflective cracking mitigation methods for an asphalt concrete overlay over flexible pavements

Abstract Reflective Cracking (RC) has been a daunting challenge in pavement maintenance and rehabilitation (M&R), yet, still, after several decades of research, no exclusive solution prevails. Moreover, RC mitigation methods have shown significant variation in in situ performance. Therefore, a technique tailored to select an effective RC mitigation method is essential for the success of pavement M&R. In this study, a life cycle cost (LCC) and multi-criteria decision-making (MCDM) analyses were conducted to evaluate the effectiveness of currently available RC mitigation methods and to select the optimal method for an asphalt concrete overlay above flexible pavements. The MCDM includes three components: LCC, performance, and materials (recyclability). These criteria determine the selection ranking of each RC mitigation method. In addition, the effects of the priority level including cost, performance, and recyclability on the final decision were evaluated by conducting a series of sensitivity analysis under multiple scenarios; therefore, weight combination of the three criteria were recorded to define the measurements affecting the final decision.

Improved rolling dynamic deflectometer for continuous pavement deflection measurements

Unlike discrete testing methods, the rolling dynamic deflectometer (RDD) performs continuous measurements. Thus, it is a powerful screening and evaluation tool for quickly characterizing large sections of highway and airfield pavements with little danger of missing critical pavement features. RDD testing applications have involved (1) pavement forensic investigations, (2) delineations of areas to be repaired, (3) selections of rehabilitation treatments, measurements of relative improvements due to the rehabilitation, and (4) monitoring of changes with time (trafficking and environmental loading). This paper discusses the efforts to improve the velocity of RDD testing up to 5 mph (8.0 km/h) while minimizing the accuracy and resolution of deflection data. The research consisted of the development of a velocity-improved rolling sensor and the field evaluation of its new sensor system. The velocity-improved rolling sensor and the enhanced data processing were tested in both flexible and rigid pavements at varied velocities. The enhanced RDD system potentially enabled testing velocities of up to 5 mph (8.0 km/h) in thin flexible pavements (i.e., farm-to-market roads) and up to 3 mph (4.8 km/h) in rigid pavements.

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.

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.

Experimental Study on Sinkholes: Soil–Groundwater Behaviors Under Varied Hydrogeological Conditions

Sinkholes have been one of the major geohazards in karst terrain and have resulted in loss of human life, as well as significant civil engineering infrastructure. Approximately 20 % of the United States is underlain by karst terrain formed from the dissolution of soluble rocks, and is susceptible to a sinkhole hazard. Particularly, Texas, Florida, Tennessee, Alabama, Missouri, Kentucky, and Pennsylvania are known as sinkhole states. Surprisingly, the understanding of sinkholes is still poor in geotechnical engineering. This paper presents and discusses a preliminary study on the mechanism of Floridas sinkholes that are triggered by groundwater flow. A physical soil–groundwater model was devised, and multiple tests were conducted under different hydrogeological conditions (e.g., with/without aquitard and overburden soil thickness). Groundwater at multiple locations was monitored during the sinkhole-simulation process so that integrated soil–groundwater behaviors could be investigated. It is found that groundwater responds before the surface collapse (showing a cone of depression); thus, a pattern change of groundwater flow can be used as input to pre-detect a sinkhole. In addition, having a clayey sand layer within sand shows a significant influence that includes a rapid change of groundwater flow in the sinkhole process and a larger surface sinkhole.

Static pullout resistance of anchor chains in cohesionless soil—laboratory testing

ABSTRACT This paper investigates the static pullout resistance of anchor chains embedded into cohesionless soil. The anchor chains, which are made of steel, were buried into Jumunjin sand whose relative density was set to approximately 60%. The anchor chains were horizontally pulled out through a displacement of 70 mm in laboratory model tests. Three different embedment depths and seven different numbers of chain links were adopted. The pullout resistance of the anchor chains was found to increase with increasing embedment depth and the number of anchor chain links. The measured resistance was significantly higher than the calculated frictional resistance, implying that the passive resistance at the front of the anchor chain significantly contributes to the pullout resistance. The contribution of the passive resistance tends to decrease with increasing number of chain links.

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.