Stress dependent behaviour of unbound layers of unselected construction and demolition waste aggregates by lightweight deflectometer tests

The use of construction and demolition waste (CDW) aggregates in unbound road pavement layers is increasing. However, the lack of data on performance in the field has spurred this investigation into their in-situ properties. A lightweight deflectometer (LWD) is a fast and simulative testing device for estimating the elastic modulus of unbound pavement layers. A field test pit was built to run LWD measurements on an unbound subbase layer containing CDW aggregates compacted at different energy levels. To assess their stress-strain non-linear behaviour, several LWD drops were performed on the same location by varying (i) the loading mass, (ii) the drop height, and (iii) the plate diameter. A stress-hardening behaviour of in-situ CDW aggregates was observed, consistent with the stress dependent evolution of resilient modulus of granular material commonly recorded in laboratory tests. The LWD modulus was found to be dependent on the level of compaction energy but also sensitive to the mechanical response of the layer below. The outcomes at this test pit suggest it would be wise to consider the rational evaluation of the in-field stress dependent behaviour of unbound CDW granular materials at both the design stage and when devising quality acceptance procedures. Nonetheless, to have a comprehensive interpretation of LWD results a greater uniformity of material properties and a stronger control of construction procedures will be desired, especially when heterogenous materials such as CDW aggregates are investigated

Validation of a Driving Simulator for Road Tunnel Behavioural Studies

Introduction. According to European regulations, road tunnel safety is strategic in the management of national and international road corridors. Although the accident rate is lower in tunnels than on open roads, the severity of crashes in tunnels is higher due to the presence of hard lateral obstacles and limited space in case of lane departure. Driving simulation studies can support design decisions to assess the impact of any safety improvement albeit driving simulators must be validated to understand how the experimental results relate to real driving conditions. Method. This study deals with the behavioural validation of the fixed base driving simulator of the RSDS Lab for safety studies for tunnels. Field speed and lateral position data for vehicles were collected by image analysis of video sequences collected from the CCTV cameras in five sections of the Fréjus tunnel (Italy-France). The tunnel was faithfully modelled in the virtual scenario, and the same data were collected by extracting records at the same cameras’ stations. Thirty-five participants were involved in a between-subject experiment. Fifteen drivers with Italian B licenses drove a car, and twenty professional drivers with Italian C and/or D licenses drove a heavy truck. Results and Conclusions. Normality tests for data distributions and t-tests for the comparison between real and simulated data were conducted. The simulator achieved the relative validation for truck speeds (with values observed in the simulation always lower than those observed in real driving), and absolute validation with regard to truck lateral position. Opposite outcomes were obtained for cars, with absolute validity for speed and relative validity for lateral position. The relative-absolute validation of the driving simulator enables us to establish how experimental outcomes can be generalized to understand the impact of any safety countermeasure

Alternative Horizontal Markings along Curved Exit Ramp Terminals to Improve Driver-Safety-Related Performance

Previous investigation has revealed that diverging maneuvers along curved terminals lead to a deterioration in the longitudinal and transversal performances of drivers with respect to linear ones. As a countermeasure, innovative horizontal markings (HMs) may be used to compel drivers to drive more prudently and maintain better vehicle control. In this driving simulation study, the behavioral effects of alternative HMs along curved exit ramp terminals were investigated. Forty-eight voluntary par-ticipants drove along randomly assigned exit ramp terminals, the design of which involved combinations of the following input variables: (i) horizontal markings (standard HM1, with internal lane bands HM2, with external zebra stripes HM3); (ii) lighting conditions (day and night); (iii) traffic flow in the motorway (1,000 passenger cars per hour pc/h and 3,000 pc/h), and (iv) ramp terminal connection type (continuous and reverse). Longitudinal (i.e., speed) and transversal (i.e., lateral position and diverging abscissa) behavioral data were collected. HM2 leads to greater improvements in the level of road safety thanks to better longitudinal and transversal driver behavior. However, drivers did delay their exit from the motorway with respect to the baseline condition (HM1) independent of the connection type. No relevant improvements were observed with HM3, apart from speed reductions at the end of the terminal and more centered trajectories when approaching the ramp. Results also show that drivers tended to enter the reverse terminal later than the continuous one (where drivers correctly used the taper), thus revealing that the use of the innovative HMs was not able to compensate for this inappropriate behavior adopted along reverse terminals

Preliminary laboratory multi-scale investigation on performance of pervious concrete pavements and vegetated elements as storm water bio-filters and retention systems

The growing population in urban areas worldwide is having a severe impact on the environment and quality of life of inhabitants. To alleviate the impact on traditional transportation infrastructures, existing and future urban facilities must be more environmentally friendly and sustainable. One solution is to develop new “green transportation infrastructures” (GTI) as part of the urban storm water management system. Although technologies for GTI have been well-investigated, there is limited experience of their potential benefits globally and, specifically, in Italy. This work, funded by the Regione Piemonte in 2015 and supported by different areas of expertise, aimed at promoting new urban storm water systems through the retention, filtration, and restoration of natural soil water content. To this end, a laboratory investigation of porous road pavements (Figure 1), and vegetated boxes (Figure 2 and 3) that filter runoff pollutants from impervious pavements was conducted to examine ecological, hydraulic, and mechanical performance levels. Three different experimental scales (samples, columns, and boxes) for the two GTI technologies were considered. Samples were used to assess the permeability, void content, strength, and pollution reduction potential of different materials used to build full-scale bio-filter systems. The pollutant reduction was determined by the reduction in suspended solids and hydrocarbon concentration, with results confirming that it depends on filter type and permeability. The preliminary results are encouraging and show a high reduction in total suspended solids and hydrocarbon concentrations (from 65% to 99%). Concrete pervious pavements and vegetated bio-filter systems were reproduced in columns and boxes, combining materials and supports for biofilm bacteria (geotextile, plastic caps) to assess the abatement potential of pre-developed biofilm bacteria compared to systems where bacteria are present naturally. Hydraulic parameters (percolation time, void content, outflow rate) were estimated so as to provide basic design parameters for full-scale applications

Multiscale assessment of construction and demolition waste aggregates stabilization through alkaline activation

L'abstract è presente nell'allegato / the abstract is in the attachmen

Compaction and freeze-thaw degradation assessment of recycled aggregates from unseparated construction and demolition waste

Although previous studies attested to the feasibility of using recycled aggregates from unseparated construction and demolition waste (UCDW aggregates) in unbound layers of road pavements, the degradation caused by compaction and freezing action under simulative conditions has not been investigated yet. To investigate the effects of these two sources of degradation on resilient modulus (RM), three UCDW aggregates were collected from different plants in the Turin area and compared with a natural (NAT) aggregate. Partially-saturated specimens of UCDW aggregates at the optimal moisture content (wopt) and at wopt±2% were prepared at the gyratory shear compactor with 30 and 100 gyrations, and by subjecting specimens to 0, 4 and 8 two-day freeze-thaw cycles from −18 °C to +20 °C. Brittle and weak components of UCDW aggregates (crushed concrete, bricks) generate fine particles in the first part of the compaction process (in the first 30 gyrations). Freeze-thaw action led to a clear increase in the resilient modulus of UCDW specimens compacted at wopt and wopt+2%. A similar trend in RM was observed in the case of NAT aggregate in similar moisture conditions, while both UCDW and NAT exhibited a slight decrease for some samples prepared at wopt−2%. Under more severe but non-simulative testing conditions such as those currently used to select conventional granular materials, UCDW aggregate exhibits lower performances than NAT aggregate. Conversely, when evaluated in more simulative test conditions, the behaviour of UCDW aggregate is comparable to that of NAT one

Short-Term and Long-Term Effects of Cement Kiln Dust Stabilization of Construction and Demolition Waste

High volumes of construction and demolition waste (CDW) are continuously produced worldwide. The European Commission aims to increase the recycling of nonhazardous CDW to a minimum of 70% in weight terms by 2020. Hence, there is increasing pressure on researchers to focus on the valorization of these alternative materials for use in the world of construction alongside traditional materials. CDW contains materials from excavation and/or demolition and are typically heterogeneous in terms of composition, grain size, and toughness; furthermore, some particles are more sensitive to degradation processes than others. One solution for an increase in durability while maintaining sufficient strength levels is chemical stabilization with cementitious binders. The paper illustrates the results of a laboratory investigation into the properties of CDW when subject to stabilization with cement kiln dust (CKD). Mixtures of CDW stabilized with ordinary portland cement (OPC) were prepared for comparison purposes. The results obtained with CKD are encouraging because it increases the strength and stiffness of CDW, thus leading to a material completely made up of recycled wastes and by-products usable in the formation of pavement subbases and subgrades. As regards the curing time, all mixtures saw a significant increase in their mechanical parameters when passing from 7-28 days to 365 days of curing

Life Cycle Economic and Environmental Impacts of CDW Recycled Aggregates in Roadway Construction and Rehabilitation

The use of recycled materials in roadway construction and rehabilitation can achieve significant benefits in saving natural resources, reducing energy, greenhouse gas emissions and costs. Construction and demolition waste (CDW) recycled aggregate as an alternative to natural one can enhance sustainability benefits in roadway infrastructure. The objective of this study was to quantitatively assess the life cycle economic and environmental benefits when alternative stabilized-CDW aggregates are used in pavement construction. Comparative analysis was conducted on a pavement project representative of typical construction practices in northern Italy so as to quantify such benefits. The proposed alternative sustainable construction strategies considered CDW aggregates stabilized with both cement and cement kiln dust (CKD) for the base layer of the roadway. The life cycle assessment results indicate that using CDW aggregate stabilized with CKD results in considerable cost savings and environmental benefits due to (i) lower energy consumption and emissions generation during material processing and (ii) reduction in landfill disposal. The benefits illustrated in this analysis should encourage the wider adoption of stabilized CDW aggregate in roadway construction and rehabilitation. In terms of transferability, the analysis approach suggested in this study can be used to assess the economic and environmental benefits of these and other recycled materials in roadway infrastructure elsewhere