This paper describes a study that used permeability measurement along with physical and hydrological characteristics of 20 pervious concrete pavements in parking lots throughout California. The ...permeability was measured at five locations: the main entrance, an area with no traffic, and three separate measurements within a parking space at each parking lot. Hydrological and physical site characteristics such as traffic flow, erosion, vegetation cover, sediments accumulation, maintenance practice, presence of cracking, rainfall, and temperature data were also collected for each parking lot. These data were used to perform detailed statistical analysis to determine factors influencing changes in permeability and hence assessing possible cause of clogging. In addition, seven representative core samples were obtained from four different parking lots with permeability ranging from very low to very high. Porosity profiles produced from CT scanning were used to assess the possible nature and extent of clogging.
Results showed that there is a large variation in permeability within each parking lot and between different parking lots. In general, the age of the parking lot is the predominant factor influencing the permeability. Statistical analysis revealed that fine sediment (particles less than 38
μm) mass is also an important influencing factor. Other influencing factors with lower significance included number of days with a temperature greater than 30
°C and the amount of vegetation next to the parking lot. The combined scanned image analysis and porosity profile of the cores showed that most clogging occurs near the surface of the pavement. While lower porosity generally appeared to be limited to the upper 25
mm, in some core samples evidence of lower porosity was found up to 100
mm below the surface.
► Twenty pervious parking lots were used to investigate possible clogging. ► Hydraulic conductivity within each parking lot was substantially different. ► Hydraulic conductivity of older parking lots was lower than newer parking lots. ► Two dominant factors influencing the hydraulic conductivity were pavement age and particles <38
μm. ► Scan image showed that the porosity of the top 25
mm was generally lower and may be the cause of clogging.
► We determined the changes in asphalt concrete (AC) microstructure under trafficking. ► We determined the contribution of densification to total accumulated AC rutting. ► Majority of densification ...is occurring at the bottom of construction lift for the PG64-28PM mix. ► A significant shear flow pattern in the direction of traffic was observed for RHMA-G test sections. ► Earlier failure of RHMA-G is due to the gradation and aggregate size induced excessive shear flow.
In this study, a new approach was used to evaluate changes in asphalt concrete microstructure under full-scale accelerated pavement test loading with a Heavy Vehicle Simulator (HVS) of composite pavement. The approach compared X-ray computed tomography (CT) images taken before and after HVS rut testing. Results were used to identify the differences in the movement of aggregate and changes in air-void content and distribution occurring during rutting accumulation of rubberized gap graded and polymer modified dense graded mixes for two overlay thicknesses (64 and 114mm). Although high air void content for the sections constructed with rubberized gap graded mix were expected to cause more densification related rutting and earlier failure related to this densification, the actual reason behind the earlier failure was determined to be primarily greater shear flow to the sides of the wheelpath associated with the gap gradation and small aggregate size. Significant movement of aggregate was observed in the direction of travel as well as to the side under the pushed wheel. Important differences in aggregate movement and air-void changes were also observed between different overlay thicknesses indicating the depth of the rut phenomenon, important information for the design of overlays on aged asphalt concrete as well.
In this study, predictions of full-scale micromechanical (MM) finite element (FE) models, developed from X-ray computed tomography images of asphalt concrete samples that were sawn from the ...accelerated pavement test sections, were used to evaluate the accuracy of layered elastic theory (LET) models that are used in pavement design today. First, MM FE and LET models were both calibrated using the measured strain gauge responses. Predictions of calibrated models were compared to evaluate the reasonableness of LET model outputs at high temperatures. Second, asphalt concrete stiffnesses measured in the laboratory were directly used for LET model development without performing any strain gauge calibration to evaluate the actual predictive capability of LET models in pavement design by using the calibrated MM FE model outputs as the ground truth. Recommendations were also made for future use of the MM FE models to improve the predictive capability of LET models.
To describe the lymphatic drainage patterns of the human eyelids.
Twenty-eight consenting patients who underwent unilateral eyelid surgery at McMaster University between March 2001 and July 2003 had ...their contralateral eyelids injected with 0.2 ml (0.250 mCi) of Tc 99 m sulphur colloid. The patients were divided into 1 of 5 injection sites of the eyelid, namely upper lateral, upper medial, medial canthus, lower medial, and lower lateral. Lymphoscintigraphy was performed between 2 and 6 hours later with a conventional planar gamma camera. Nodes in the head and neck were identified. In 15 patients, the right eye was injected, and in 13 patients, the left eye was injected.
Three patients had no nodes that were identifiable. The remaining 25 patients had at least one node identified. In 11 patients, more than one node was identified. In 18 patients, the preauricular node was most intense and recognized first. Regardless of location on the eyelid, the sentinel node was most commonly the preauricular node.
These results conflict with previously described classic drainage patterns of the eyelid lymphatics. In 72% (18/25) of cases, the first-order sentinel node was the preauricular node, regardless of location of the injection site on the eyelid. Many individuals did not fit the classic drainage patterns.
Purpose To determine the success rate of nasolacrimal duct probing for the treatment of congenital nasolacrimal duct obstruction and to identify the age at which the success rate decreases. Methods ...Records for probing procedures from 2005 to 2010, over a 56-month period, were reviewed. Successful probing was defined as complete resolution of epiphora 3 months after treatment. Success rates were compared between children <3 years of age and children ≥3 years of age at the time of the procedure. Results A total of 168 eyes (128 children, mean age 32.2 ± 23.8 months) had undergone a probing procedure, and the overall success rate was 72%. Children aged <36 months had a success rate of 78%; children aged ≥36 months had a success rate of 50%. Multivariate analysis demonstrated that age at the time of procedure was a significant risk factor for failed probing ( P = 0.035; OR, 1.67; 95% CI, 1.04-2.69), whereas sex and bilateral surgery were not. Conclusions The success rate of primary probing for congenital nasolacrimal duct obstruction was significantly reduced when performed on children ≥3 years of age.
•Bio-derived ashes, such as rice hull and rice straw ash, can be used in concrete.•Use of rice straw ash is not as well analyzed as rice hull ash in concrete.•Use of rice hull ash in concrete can ...improve certain mechanical properties.•Further analysis is necessary to understand the effects on concrete durability.•Additional analysis is needed to quantify environmental and economic impacts.
The demand for concrete continues to grow with increases in population and increased urbanization. This demand, in turn, increases the need to reduce the environmental impacts of concrete while continuing to provide the same or better performance. Increasing population also creates growing demand for food and energy resources. The cultivation of rice, the staple food of over half the world's inhabitants, results in the production of additional biomass. Rice biomass, such as hulls and straw, can be combusted as a renewable energy source and, under specific combustion conditions, the resulting ash can be used as a supplementary cementitious material or beneficial filler in the production of concrete, which can potentially lead to reduced environmental impacts in concrete.
This paper reviews rice-based ash and its influence on concrete properties to address current understanding of these ashes as an alternative mineral admixture. The review of the literature shows that under proper combustion conditions as well as through use of pre- and post-combustion treatments, highly pozzolanic (reactive) ash can be produced from rice hulls. These reactive ashes have the ability to improve several properties of concrete when used as a partial replacement for cement. Additionally, the production of rice-based ash can offer a lower greenhouse gas emitting pozzolan than portland cement and some conventional supplementary cementitious materials. Further research into the utilization of rice-straw ash, durability properties, and high performance concrete could lead to the production of rice ash as a cost- and environmentally-competitive alternative in the production of concrete.
With the rapid development of cities, more attention has been paid to the stormwater runoff pollution on roads. In this paper, a kind of photocatalytic water purification pavement coated with ...nano-TiO2was developed, which could improve the water purification performance of porous concrete. Through removal rate analysis of three typical pollutants, the improvement of its water purification performance was evaluated. The skid resistance of road surface and durability of purification effect were also studied by using pendulum apparatus and artificial accelerated aging method. The results showed that the removal rates of COD, TP and NH3-N could reach 50%, 60% and 40%, respectively. The application of photocatalytic coating would reduce skid resistance of pavement relatively. Besides, appropriate increase of nano-TiO2content will improve the weather resistance. This study will provide useful insights for the preparation of nano-TiO2photocatalytic coatings for porous cement concrete to improve the water purification effect of roads.
Fully permeable pavement is gradually gaining support as an alternative best management practice (BMP) for stormwater runoff management. As the use of these pavements increases, a definitive test ...method is needed to measure hydraulic performance and to evaluate clogging, both for performance studies and for assessment of permeability for construction quality assurance and maintenance needs assessment. Two of the most commonly used permeability measurement tests for porous asphalt and pervious concrete are the National Center for Asphalt Technology (NCAT) permeameter and ASTM C1701, respectively. This study was undertaken to compare measured values for both methods in the field on a variety of permeable pavements used in current practice. The field measurements were performed using six experimental section designs with different permeable pavement surface types including pervious concrete, porous asphalt and permeable interlocking concrete pavers. Multiple measurements were performed at five locations on each pavement test section. The results showed that: (i) silicone gel is a superior sealing material to prevent water leakage compared with conventional plumbing putty; (ii) both methods (NCAT and ASTM) can effectively be used to measure the permeability of all pavement types and the surface material type will not impact the measurement precision; (iii) the permeability values measured with the ASTM method were 50–90% (75% on average) lower than those measured with the NCAT method; (iv) the larger permeameter cylinder diameter used in the ASTM method improved the reliability and reduced the variability of the measured permeability.
► This study compares the permeability measured by ASTM C1701 and NCAT methods. ► Mix design and binder type did not significantly impact the measurement precision. ► Strong correlation (R2 > 0.72) was observed between the two measurement methods. ► Permeability values measured by the ASTM were generally 50–90% lower than the NCAT method. ► Larger permeameter diameter used in the ASTM reduced the measurement variability.
In Keynes' model, no variety of private sector spending plays a more critical role than investment. This is so because reaching full employment requires that it be large enough to offset the volume ...of saving that would be forthcoming at that level of economic activity, which occurs only rarely and by coincidence. Despite its key role, very few Post Keynesians have undertaken empirical studies of Keynes' approach (as opposed to one based on Keynes). While I suspect that there are a number of reasons for this, perhaps the greatest stumbling block is one related to data: how do we measure not just investors' expectations, but the difference between what was expected and what actually transpired? I believe I have developed a defensible solution to this problem, one that not only allows for a more direct test of Keynes' theory but also offers tremendous support for it.
